Methods and equations for analysing the kinetics of enzyme-catalysed reactions were developed at the beginning of the 20th century in two centres in particular; in Paris, by Victor Henri, and, in Berlin, by Leonor Michaelis and Maud Menten. Henri made a detailed analysis of the work in this area that had preceded him, and arrived at a correct equation for the initial rate of reaction. However, his approach was open to the important objection that he took no account of the (...) hydrogen-ion concentration (a subject largely undeveloped in his time). In addition, although he wrote down an expression for the initial rate of reaction and described the hyperbolic form of its dependence on the substrate concentration, he did not appreciate the great advantages that would come from analysis in terms of initial rates rather than time courses. Michaelis and Menten not only placed Henri's analysis on a firm experimental foundation, but also defined the experimental protocol that remains standard today. Here, we review this development, and discuss other scientific contributions of these individuals. The three parts have different authors, as indicated, and do not necessarily agree on all details, in particular about the relative importance of the contributions of Michaelis and Menten on the one hand and of Henri on the other. Rather than force the review into an unrealistic consensus, we consider it appropriate to leave the disagreements visible. (shrink)

The acidity function is a thermodynamic quantitative measure of acid strength for non-aqueous and concentrated aqueous Brønsted acids, with acid strength being defined as the extent to which the acid protonates a base of known basicity. The acidity function, which was developed, both theoretically and experimentally, by Louis P. Hammett of Columbia University during the 1930s, has proven useful in the area of physical organic chemistry where it has been used to correlate rates of acid-catalyzed reactions and to quantitate the (...) acidity of superacids, acids with protonating abilities greater than pure sulfuric acid. All Brønsted acids can now be compared using a common measure. Karl Popper’s seminal idea of theory falsification does not apply here because of the many successful applications of the acidity function. Likewise, Thomas Kuhn’s idea of a paradigm shift does not apply here, even though the acidity function concept was revolutionary, because the acidity function is commensurate with classical concepts of acidity. (shrink)

The Earth agglomerates and heats. Convection cells within the planetary interior expedite the cooling process. Volcanoes evolve steam, carbon dioxide, sulfur dioxide and pyrophosphate. An acidulous Hadean ocean condenses from the carbon dioxide atmosphere. Dusts and stratospheric sulfurous smogs absorb a proportion of the Sun’s rays. The cooled ocean leaks into the stressed crust and also convects. High temperature acid springs, coupled to magmatic plumes and spreading centers, emit iron, manganese, zinc, cobalt and nickel ions to the ocean. Away from (...) the spreading centers cooler alkaline spring waters emanate from the ocean floor. These bear hydrogen, formate, ammonia, hydrosulfide and minor methane thiol. The thermal potential begins to be dissipated but the chemical potential is dammed. The exhaling alkaline solutions are frustrated in their further attempt to mix thoroughly with their oceanic source by the spontaneous precipitation of biomorphic barriers of colloidal iron compounds and other minerals. It is here we surmise that organic molecules are synthesized, filtered, concentrated and adsorbed, while acetate and methane—separate products of the precursor to the reductive acetyl-coenzyme-A pathway—are exhaled as waste. Reactions in mineral compartments produce acetate, amino acids, and the components of nucleosides. Short peptides, condensed from the simple amino acids, sequester ‘ready-made’ iron sulfide clusters to form protoferredoxins, and also bind phosphates. Nucleotides are assembled from amino acids, simple phosphates carbon dioxide and ribose phosphate upon nanocrystalline mineral surfaces. The side chains of particular amino acids register to fitting nucleotide triplet clefts. Keyed in, the amino acids are polymerized, through acid–base catalysis, to alpha chains. Peptides, the tenuous outer-most filaments of the nanocrysts, continually peel away from bound RNA. The polymers are concentrated at cooler regions of the mineral compartments through thermophoresis. RNA is reproduced through a convective polymerase chain reaction operating between 40 and 100°C. The coded peptides produce true ferredoxins, the ubiquitous proteins with the longest evolutionary pedigree. They take over the role of catalyst and electron transfer agent from the iron sulfides. Other iron–nickel sulfide clusters, sequestered now by cysteine residues as CO-dehydrogenase and acetyl-coenzyme-A synthase, promote further chemosynthesis and support the hatchery—the electrochemical reactor—from which they sprang. Reactions and interactions fall into step as further pathways are negotiated. This hydrothermal circuitry offers a continuous supply of material and chemical energy, as well as electricity and proticity at a potential appropriate for the onset of life in the dark, a rapidly emerging kinetic structure born to persist, evolve and generate entropy while the sun shines. (shrink)

The direction and specificity of endolysosomal membrane trafficking is tightly regulated by various cytosolic and membrane‐bound factors, including soluble NSF attachment protein receptors (SNAREs), Rab GTPases, and phosphoinositides. Another trafficking regulatory factor is juxta‐organellar Ca2+, which is hypothesized to be released from the lumen of endolysosomes and to be present at higher concentrations near fusion/fission sites. The recent identification and characterization of several Ca2+ channel proteins from endolysosomal membranes has provided a unique opportunity to examine the roles of Ca2+ and (...) Ca2+ channels in the membrane trafficking of endolysosomes. SNAREs, Rab GTPases, and phosphoinositides have been reported to regulate plasma membrane ion channels, thereby suggesting that these trafficking regulators may also modulate endolysosomal dynamics by controlling Ca2+ flux across endolysosomal membranes. In this paper, we discuss the roles of phosphoinositides, Ca2+, and potential interactions between endolysosomal Ca2+ channels and phosphoinositides in endolysosomal dynamics. (shrink)

An in-situ transmission electron microscopy straining technique has been used to investigate the dynamics of dislocation-defect interactions in ion-irradiated copper and the subsequent formation of defect-free channels. Defect removal frequently required interaction with multiple dislocations, although screw dislocations were more efficient at annihilating defects than edge dislocations were. The defect pinning strength was determined from the dislocation curvature prior to breakaway and exhibited values ranging from 15 to 175 MPa. Pre-existing dislocations percolated through the defect field but did not show (...) long-range motion, indicating that they are not responsible for creating the defect-free channels and have a limited contribution to the total plasticity. Defect-free channels were associated with the movement of many dislocations, which originated from grain boundaries or regions of high stress concentration such as at a crack tip. These experimental results are compared with atomistic simulations of the interaction of partial dislocations with defects in copper and a dispersed-barrier-hardening crystal plasticity model to correlate the observations to bulk mechanical properties. (shrink)

The ciliated protozoan, Paramecium, broadcasts the activity of its individual ion channel classes through its swimming behaviour. This fact has made it possible to isolate mutants with defective ion currents, simply by selecting individuals with abnormal swimming patterns. At least four of Paramecium's ion currents are activated by rising intracellular calcium concentration, including two K+ currents and a Na+ current. A variety of cell lines with defects in these Ca2+‐dependent currents have been isolated: in several cases, the defects have (...) been traced to mutations in the structural gene for calmodulin. Sequence analysis of calmodulins from these and other Ca2+ ‐dependent ion‐current mutants may enable a detailed mapping of putative channel interaction domains on the surface of the calmodulin molecule. (shrink)

Animals and plants can be classified into three distinct groups according to their pH- and pO-values and the ratios of inorganic ion concentrations and organic molecule concentrations in their intracellular or extracellular saps . The origin of these types could be sought in the evolutionary change from aquatic to terrestrial environment. The widespread existence of these types in nature enables a direct comparison between the physicochemical composition of consumer and its producer. An example of such relationship was found in the (...) order Hemiptera. No symbiosis exists when the consumer and producer belong to the same physicochemical type. On the other hand, if the types differ, extra- or intracellular symbiosis are usually found to exist. The conclusion is drawn that endosysmbiosis provides means for the compensation of this difference. (shrink)

In photoreceptors of a dark adapted eye, the inward flux of sodium and calcium ions in the outer segment is balanced by the outward flux of potassium ions. But in the presence of light the creation of cyclic guanosine monophosphate in the outer segment decreases. Due to low concentration of cG the channels in the outer segment open relatively less and thus the influx of calcium ion decreases, leading finally to hyperpolarization of the photoreceptors. We have analyzed theoretically the (...) effect of oxidizing iron ions on the photoreceptors. In order to explain the effects of iron-induced oxidative stress, the different molecules and ions involved in phototransduction are quantified leading to a differential equation for calculating the electroretinogram a-wave voltage. The theoretical results are compared with published experimental data. In the presence of light, the iron ions could push outward the similarly charged calcium ions resulting in a small increase in the amount of inward calcium flux. Again, the presence of iron ions generates Reactive Oxygen Species, and ROS could attract the calcium ions which also increases the calcium flux. This will result in a reduction in the amplitude and slope of the a-wave voltage in the electroretinogram. These results are parametrized in terms of calcium ion concentrations. As the amplitude of the a-wave shows how much electrical signal is produced, its reduction indicates reduction in the visual signal. Thus, the increase in iron ions could explain the reduction in the electrical signal due to iron-induced oxidative stress. (shrink)

Calcium plays an important role in regulating a great variety of neuronal processes, and many efforts are made to generate gadolinium complexes that can act as calcium-dependent MRI contrast agents. A series of gadolinium chelate complexes based on DO3A were developed, bearing phosphonate groups as an additional coordination sites, which is hypothesized to change relaxivity in magnetic resonance experiments dynamically with Ca2+ concentration. Different lengths of the phosphonate side chains are expected to lead to different binding constants of the (...) phosphonate - gadolinium bonds. The latter property can be exploited for fine-tuning the sensitivity of the agent to calcium ion concentration. (shrink)

In order to make an attempt at grouping the various aspects of brain functional imaging (fMRI, MRS, EEG-MEG, ...) within a coherent frame, we implemented a model consisting of a system of differential equations, that includes: (1) sodium membrane transport, (2) Na/K ATPase, (3) neuronal energy metabolism (i.e. glycolysis, buffering effect of phosphocreatine, and mitochondrial respiration), (4) blood-brain barrier exchanges and (5) brain hemodynamics, all the processes which are involved in the activation of brain areas. We assumed that the correlation (...) between brain activation and metabolism could be due to either changes in the concentrations of ATP and ADP following activation of Na/K ATPase that result from the changes in ion concentrations, or the involvement, in different phases of metabolism, of a second messenger such as calcium. In this article, we show how this type of model enables interpretation of MRS and fMRI published data that were obtained during prolonged stimulations. (shrink)

There exist two methods for finding the magnetic moment of the electron. The first method employed in quantum electrodynamics consists in calculating the energy of the electron placed in a constant magnetic field, the extra energy due to the field being proportional to the magnetic moment. It is also possible to use the second method proceeding from the fact that the asymptotic form of the vector potential at infinity is proportional to the magnetic moment. If the electron were point-like, both (...) the methods would yield identical results. In the present paper is studied the magnetic field created by the electron in hydrogen-like ions, which enables one to find the electron magnetic moment by the second method. The electron magnetic moment in this case proves to be different in different states of the electron in the Coulomb field of the ions and, moreover, is distinct from the magnetic moment calculated by the first method. The results of the paper show that the electron is not small and is deformable under action of external fields. (shrink)

Despite thermodynamic, bioenergetic and phylogenetic failings, the 81‐year‐old concept of primordial soup remains central to mainstream thinking on the origin of life. But soup is homogeneous in pH and redox potential, and so has no capacity for energy coupling by chemiosmosis. Thermodynamic constraints make chemiosmosis strictly necessary for carbon and energy metabolism in all free‐living chemotrophs, and presumably the first free‐living cells too. Proton gradients form naturally at alkaline hydrothermal vents and are viewed as central to the origin of life. (...) Here we consider how the earliest cells might have harnessed a geochemically created proton‐motive force and then learned to make their own, a transition that was necessary for their escape from the vents. Synthesis of ATP by chemiosmosis today involves generation of an ion gradient by means of vectorial electron transfer from a donor to an acceptor. We argue that the first donor was hydrogen and the first acceptor CO2. (shrink)

Freely falling point-like objects converge toward the center of the Earth. Hence the gravitational field of the Earth is inhomogeneous, and possesses a tidal component. The free fall of an extended quantum mechanical object such as a hydrogen atom prepared in a high principal-quantum-number state, i.e. a circular Rydberg atom, is predicted to fall more slowly than a classical point-like object, when both objects are dropped from the same height above the Earth’s surface. This indicates that, apart from transitions (...) between quantum states, the atom exhibits a kind of quantum mechanical incompressibility during free fall in inhomogeneous, tidal gravitational fields like those of the Earth.A superconducting ring-like system with a persistent current circulating around it behaves like the circular Rydberg atom during free fall. Like the electronic wavefunction of the freely falling atom, the Cooper-pair wavefunction is quantum mechanically incompressible. The ions in the lattice of the superconductor, however, are not incompressible, since they do not possess a globally coherent quantum phase. The resulting difference during free fall in the response of the nonlocalizable Cooper pairs of electrons and the localizable ions to inhomogeneous gravitational fields is predicted to lead to a charge separation effect, which in turn leads to a large Coulomb force that opposes the convergence caused by the tidal gravitational force on the superconducting system.A “Cavendish-like” experiment is proposed for observing the charge separation effect induced by inhomogeneous gravitational fields in a superconducting circuit. The charge separation effect is determined to be limited by a pair-breaking process that occurs when low frequency gravitational perturbations are present. (shrink)

The paper is aimed at rationalizing relationships between the structure of inorganic compounds in condensed phases and their melting and boiling points. It is documented that the main factor governing both points is their molecular or polymeric nature. In case of polymeric ionic compounds, the higher actual charge bearing by the ions involved, the higher their melting/boiling points. In case of covalent polymers, the value of both points increases with polymer dimensionality and with the number and energy of the respective (...) covalent bonds. In case of molecular compounds, both points depend on the weight and shape of molecules, the presence of hydrogen bonds, and electric quadrupole moment. (shrink)

The Bohr formulation—the original one—is now largely a matter of history. The usual career of a theory was its fate. It explained much, but it failed at the first signs of complication, even for the simplest molecules as hydrogen and helium. Some results were either only approximate in a loose or incomplete fashion, e.g. in the application of the correspondence principle to intensities, the only reliable predictions being only for an absence of certain lines, or they quite disagreed with (...) experiment, e.g. in the case of the hydrogen molecule and the hydrogen molecule ion, the normal and excited states of helium, the anomalous Zeeman effect, the Ramsauer effect, and in the treatment of problems where more than one electron was involved. In the last mentioned cases the perturbation method, so successful in solving “many-body” problems in celestial mechanics, failed completely because systems of several electrons, possessing frequencies of the order of light waves, cannot interact classically. A bit of much forced pragmatism was practiced in treating the many electron atom as a variation of the hydrogen atom. Besides, there were technical oddities, like ½ quantum numbers, and impenetrated anologies between visible and X-ray spectra. (shrink)

No exact definition of an “organic” substance has been agreed upon by the chemical community and textbook definitions vary substantially. The question of what exactly constitutes an “organic” substance is explored in this paper. Various carbon-containing substances that have been by some considered to be “inorganic” are examined in an attempt to ascertain whether carbon in these compounds display different chemical behavior than what is expected of carbon in an “organic” substance. Types of substances considered are carbon allotropes, carbides, carbonates (...) and bicarbonates, cyanide and cyanate ions, carbido clusters, carbon oxides, and compounds without hydrogen.Graphic abstract. (shrink)

The high prevalence of cardiovascular diseases demands a reliable and sensitive risk assessment technique. In order to develop a fast and label-free immunosensor for C-reactive protein, a risk factor for this condition, anti-CRP antibodies were physically adsorbed to the hydrogen -terminated surface of nanocrystalline diamond. An Enzyme-Linked ImmunoSorbent Assay reference technique showed that this was a suitable substrate for antibody-antigen recognition reactions. Electrochemical Impedance Spectroscopy was used to electronically detect CRP recognition. The specificity of the immunosensor was demonstrated by (...) incubation with CRP and plasminogen as reference molecule. A different impedance behavior was observed in real-time after CRP addition as compared to plasminogen addition: the impedance increased only during CRP incubation. Fitting the data showed that this corresponded with a decrease in capacitance of the molecular layer due to its increased thickness by specific CRP recognition. Sensitivity experiments in real-time showed a clear discrimination between 1 μM, 100 nM, and 10 nM of CRP after 10 min at 100 Hz. Since, 10 nM of CRP was still clearly distinguishable from buffer solution, our CRP-directed immunosensor prototype reaches a sensitivity that is within the physiologically relevant concentration range of this biomarker in healthy controls and CVD patients. Moreover, this prototype displayed real-time discriminating power between spiked and unspiked serum, and thus also shows its applicability in this biological matrix. © 2011 Elsevier B.V. All rights reserved. (shrink)

Arbuscular mycorrhizal fungi are considered as a potential biotechnological tool for improving phytostabilization efficiency and plant tolerance to heavy metal-contaminated soils. However, the mechanisms through which AMF help to alleviate metal toxicity in plants are still poorly understood. A greenhouse experiment was conducted to evaluate the effects of two AMF species on the growth, Pb accumulation, photosynthesis and antioxidant enzyme activities of a leguminous tree at Pb addition levels of 0, 500, 1000 and 2000 mg kg-1 soil. AMF symbiosis decreased (...) Pb concentrations in the leaves and promoted the accumulation of biomass as well as photosynthetic pigment contents. Mycorrhizal plants had higher gas exchange capacity, non-photochemistry efficiency, and photochemistry efficiency compared with non-mycorrhizal plants. The enzymatic activities of superoxide dismutase, ascorbate peroxidases and glutathione peroxidase were enhanced, and hydrogen peroxide and malondialdehyde contents were reduced in mycorrhizal plants. These findings suggested that AMF symbiosis could protect plants by alleviating cellular oxidative damage in response to Pb stress. Furthermore, mycorrhizal dependency on plants increased with increasing Pb stress levels, indicating that AMF inoculation likely played a more important role in plant Pb tolerance in heavily contaminated soils. Overall, both F. mosseae and R. intraradices were able to maintain efficient symbiosis with R. pseudoacacia in Pb polluted soils. AMF symbiosis can improve photosynthesis and reactive oxygen species scavenging capabilities and decrease Pb concentrations in leaves to alleviate Pb toxicity in R. pseudoacacia. Our results suggest that the application of the two AMF species associated with R. pseudoacacia could be a promising strategy for enhancing the phytostabilization efficiency of Pb contaminated soils. (shrink)

In Minkowski flat space-time, it is perceived that time inversion is unitary rather than antiunitary, with energy being a time vector changing sign under time inversion. The Dirac equation, in the case of electromagnetic interaction, is not invariant under unitary time inversion, giving rise to a “Klein paradox.” To render unitary time inversion invariance, a nonlinear wave equation is constructed, in which the “Klein paradox” disappears. In the case of Coulomb interaction, the revised nonlinear equation can be linearized to give (...) energy solutions for Hydrogen-like ions without singularity when nuclear number Z>137, showing a reversed energy order pending for experimental tests such as Zeeman effects. In non-relativistic limit, this nonlinear equation reduces to nonlinear Schrödinger equation with soliton-like solutions. Moreover, particle conjugation and electron-proton scattering with a nonsingular current-potential interaction are discussed. Finally the explicit form of gauge function is found, the uniqueness of Lorentz gauge is proven and the Lagrangian density of quantum electrodynamics (QED) is revised as well. The implementation of unitary time inversion leads to the ultimate derivation of nonlinear QED. (shrink)

Despite thermodynamic, bioenergetic and phylogenetic failings, the 81‐year‐old concept of primordial soup remains central to mainstream thinking on the origin of life. But soup is homogeneous in pH and redox potential, and so has no capacity for energy coupling by chemiosmosis. Thermodynamic constraints make chemiosmosis strictly necessary for carbon and energy metabolism in all free‐living chemotrophs, and presumably the first free‐living cells too. Proton gradients form naturally at alkaline hydrothermal vents and are viewed as central to the origin of life. (...) Here we consider how the earliest cells might have harnessed a geochemically created proton‐motive force and then learned to make their own, a transition that was necessary for their escape from the vents. Synthesis of ATP by chemiosmosis today involves generation of an ion gradient by means of vectorial electron transfer from a donor to an acceptor. We argue that the first donor was hydrogen and the first acceptor CO2. (shrink)

As calcium plays an important role in regulating a great variety of neuronal processes, there is a strong interest to generate gadolinium complexes which can act as calcium-sensors in magnetic resonance imaging (MRI). Here we report a new series of potential CAs based on DO3A, having alkylaminobis(methylenephosphonate) side chains (propyl L1, butyl L2, pentyl L3 or hexyl L4). The high complexation efficiency towards the biologically important metal ions of the aminopolyphosphonic acids could be used for the sensing of the extracellular (...) calcium in the brain. On the other hand the introduction of negatively charged phosphonate groups into common Gd3+-based CAs increases their r1 which is important to improve the MR signal especially in high field magnets. The paramagnetic response of the complexes GdL1-GdL4 to Ca2+ was studied by means of relaxometric titrations. The initial relaxivities of the complexes found to be higher than usually reported for the DO3A type ligands at high field magnets (9.4T). r1 values of 6.92, 7.43, 6.70 and 5.76 mM-1s-1 were determined for GdL1, GdL2, GdL3, and GdL4 respectively. Interestingly complexes exhibit unusual properties in the presence of Ca2+. In contrast to previously reported probes the longitudinal relaxivities decrease upon addition of Ca2+. This is favourable for novel fMRI techniques as it could allow transforming the real in vivo decrease in Ca2+ concentration into a positive contrast during physiological processes. The sensitivity of the complexes towards Ca2+ increases with the extension of the aliphatic side chain. No changes in r1 of GdL1 were found over the whole span of Ca2+ concentration. In the case of GdL2, a moderate decrease of r1 was observed on addition of Ca2+, whereas the r1 of the GdL3 and GdL4 solutions showed a strong dependency on the calcium concentration resulting in the decrease to 66% and 61% of the initial r1 values, respectively. (shrink)

Light can kill the photoreceptors of the eye, not only very bright direct sunlight, but more moderate illumination if the light is present continuously. Recent experiments show that rod apoptosis can be triggered by strong and constant activation of transduction, and that death can be prevented if transduction is inhibited even though the eye is illuminated. Vitamin A deficiency and genetically inherited diseases, such as some forms of retinitis pigmentosa and Leber congenital amaurosis, appear to kill like this: transduction is (...) activated at a high rate and continuously, and this causes the rods to die. Why does transduction kill? Our best guess is that continuous activation produces a prolonged lowering of the Ca2+ concentration, which is also thought to kill neurons in tissue culture and during the development of the nervous system. To prevent death in constant light, rods have evolved protective mechanisms including modulation of channels and ion transport to keep the Ca2+ from going too low. Prolonged light exposure also causes migration of transduction proteins from one part of the cell to another and a reversible shortening of the rod outer segments, the part of the cell that contains the pigment rhodopsin. All of these mechanisms are at work in the normal eye to reduce transduction and prevent the Ca2+ concentration from dropping too low for too long a time. That most of us retain our vision our entire lives is a testament to their effectiveness. BioEssays 28: 344–354, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

There is now a considerable body of published work on the epistemology of modern chemistry, especially with regard to the nature of quantum chemistry. In addition, the question of the metaphysical underpinnings of chemistry has received a good deal of attention. The present article concentrates on metaphysical considerations including the question of whether elements and groups of elements are natural kinds. It is also argued that an appeal to the metaphysical nature of elements can help clarify the re-emerging controversies among (...) chemists regarding the placement of the elements hydrogen and helium in the periodic system and the question of whether there exists a best form of the periodic table. (shrink)

The dynamics of calcium in the cortical cytoplasm of plant cells has been modeled by Goodwin & Trainor (1985) using a mechanochemical field theory based on the interaction between calcium ions and the cytoskeleton. The resulting mathematical model is a system of two non-linear partial differential equations which rule the evolution of the free calcium concentration and of the cytogel strain field in the cytoplasm. According to the values of parameters such as: calcium diffusion coefficient, strength of the calcium-strain (...) coupling, gel elasticity or total calcium concentration, this system may be stable or unstable around an homogeneous equilibrium state. With the aid of numerical simulations, various kinds of solutions have been observed. When inertial forces ar neglected or for low values of the gel density, most of the solutions are asymptotically stable and are reached after a more or less complex transient. But for higher values of the volumetric density more complex solutions may exist, periodic in time and space or eventually chaotic. (shrink)

The way the central nervous system (CNS) responds to diverse stimuli is contingent upon the specific brain state of the individual, including sleep and wakefulness. Despite the wealth of readout parameters and data delineating the brain states, the primary mechanisms are yet to be identified. Here we highlight the role of astrocytes, with a specific emphasis on chloride (Cl−) homeostasis as a modulator of brain states. Neuronal activity is regulated by the concentration of ions that determine excitability. Astrocytes, as (...) the CNS homeostatic cells, are recognised for their proficiency in maintaining dynamic homeostasis of ions, known as ionostasis. Nevertheless, the contribution of astrocyte‐driven ionostasis to the genesis of brain states or their response to sleep‐inducing pharmacological agents has been overlooked. Our objective is to underscore the significance of astrocytic Cl− homeostasis, elucidating how it may underlie the modulation of brain states. We endeavour to contribute to a comprehensive understanding of the interplay between astrocytes and brain states. (shrink)

The complex sensation of vision begins with the relatively simple photoisomerization of the visual pigment chromophore 11-cis-retinal to its all-trans configuration. This event initiates a series of biochemical reactions that are collectively referred to as phototransduction, which ultimately lead to a change in the electrochemical signaling of the photoreceptor cell. To operate in a wide range of light intensities, however, the phototransduction pathway must allow for adjustments to background light. These take place through physiological adaptation processes that rely primarily on (...) Ca2+ ions. While Ca2+ may modulate some activities directly, it is more often the case that Ca2+-binding proteins mediate between transient changes in the concentration of Ca2+ and the adaptation processes that are associated with phototransduction. Recently, combined genetic, physiological, and biochemical analyses have yielded new insights about the properties and functions of many phototransduction-specific components, including some novel Ca2+-binding proteins. Understanding these Ca2+-binding proteins will provide a more complete picture of visual transduction, including the mechanisms associated with adaptation, and of related degenerative diseases. BioEssays 22:337–350, 2000. © 2000 John Wiley & Sons, Inc. (shrink)

Ferritins (FTs) are iron storage proteins that are involved in managing iron‐oxygen balance. In our work, we present a hypothesis on the putative effect of geological changes that have affected the evolution and radiation of ferritin proteins. Based on sequence analysis and phylogeny reconstruction, we hypothesize that two significant factors have been involved in the evolution of ferritin proteins: fluctuations of atmospheric oxygen concentrations, altering redox potential, and changing availability of water rich in bioavailable ferric ions.Fish, ancient amphibians, reptiles, and (...) placental mammals developed the broadest repertoire of singular FTs, attributable to embryonic growth in aquatic environments containing low oxygen levels and abundant forms of soluble iron. In contrast, oviparous land vertebrates, like reptiles and birds, that have developed in high oxygen levels and limited levels of environmental Fe2+ exhibit a lower diversity of singular FTs, but display a broad repertoire of subfamilies, particularly notable in early reptiles. (shrink)

‘Smart’ contrast agents (CA) exhibit dynamic and reversible modulation of their relaxivity by specific physiological or biochemical triggers such as changes in pH, Ca2+ concentration or enzymatic activity (1-3). The extracellular concentration of Ca2+ plays important role in physiological and pathological processes in the nervous system. This led to the designing of a chelating system in which relaxivity is influenced as a function of Ca2+ concentration by changing coordination number around the paramagnetic metal ion. We synthesized a (...) novel bifunctional bismacrocycle [Gd-(DO3A-DTPA- DO3A); Fig.] based on DO3A-EA [{4,7-Bis-carboxymethyl-10-(2-aminoethyl)-1,4,7,10-tetraazacyclododec-1-yl}-acetic acid] coupled to DTPA-bis-anhydride via a flexible alkyl spacer to form the.. (shrink)

To cope with the water deficit resulting from saline environment, plant cells accumulate three kinds of osmotica: salts, small organic solutes and hydrophillic, glycine-rich proteins. Salts such as NaCl are cheap and available but has ion toxicity in high concentrations. Small organic solutes are assistant osmotica, their main function is to protect cytoplasmic enzymes from ionic toxicity and maintain the integrity of cellular membranes. Hydrophillic, glycine-rich proteins are the most effective osmotica, they have some characteristics to avoid crystallization even in (...) high concentration, but because they are expensive they are not as commonly used as salts or organic solutes. In addition there is the question of whether the genetic information for growth in saline environment is present in all kinds of plants, both halophytes and nonhalophytes. (shrink)

Secretion systems enable bacteria to import and secrete large macromolecules including DNA and proteins. While most components of these systems have been identified, the molecular mechanisms of macromolecular transport remain poorly understood. Recent findings suggest that various bacterial secretion systems make use of the translocation ratchet mechanism for transporting polymers across the cell envelope. Translocation ratchets are powered by chemical potential differences generated by concentration gradients of ions or molecules that are specific to the respective secretion systems. Bacteria employ (...) these potential differences for biasing Brownian motion of the macromolecules within the conduits of the secretion systems. Candidates for this mechanism include DNA import by the type II secretion/type IV pilus system, DNA export by the type IV secretion system, and protein export by the type I secretion system. Here, we propose that these three secretion systems employ different molecular implementations of the translocation ratchet mechanism. Brownian ratchets are often discussed in the context of directed molecular movement. Bacterial secretion systems transport molecules through membranes in a directed fashion. Here, we focus on recent experiments supporting a role of translocation ratchets in the secretion and import of proteins and DNA. (shrink)

The frequency and temperature dependences of the ac conductivity and dielectric constant of the V 2 O 5 -MnO-TeO 2 system, containing two transition-metal ions, have been measured. The dc conductivity † dc measured in the high-temperature range decreases with addition of the oxide MnO. This is considered to be due to the formation of bonds such as V--O--Mn and Mn--O--Mn in the glass. The conductivity arises mainly from polaron hopping between V 4+ and V 5+ ions. It is found (...) that a mechanism of adiabatic small-polaron hopping is the most appropriate conduction model for these glasses. This is in sharp contrast with the behaviour of the Mn-free V 2 O 5 -TeO 2 glass, in which non-adiabatic hopping takes place. High-temperature conductivity data satisfy Mott's small-polaron hopping model and also a model proposed by Schnakenberg in 1968. A power-law behaviour † ac = A y s , with s < 1) is well exhibited by the ac conductivity † ac data of these glasses. Analysis of dielectric data indicates a Debye-type relaxation behaviour with a distribution of relaxation times. The MnO-concentration-dependent † ac data follow an overlapping large-polaron tunnelling model over the entire range of temperatures studied. The estimated model parameters are reasonable and consistent with changes in composition. (shrink)

Today a natural ball lightning (BL) phenomenon has not yet correct physical and philosophical explanation. This article is directed on a new exotic version of the occurrence and behavior of ball lightning. BL consists of a bulk air mixture—neutral air molecules, negative and positive aero ions. BL arise on linear lightning tracks due to the primary ionization of the atmosphere and the secondary effects of atmospheric light aero ions arisen. The emerging electrostatic surface tension forces form a volumetric gas drop, (...) in which the significant electrical energy of the “ball capacitor” is concentrated. The long lifetime of aero ions provides time stability of gas ball. As a rule, a BL gradually discharges and disappears due to recombination processes, emitting a weak cold glow. The explosion of BL occurs with an external destabilizing effect on its structure. First of all, this is contact with a source of free electrons—any conductive objects and surfaces, including the human body. The impulse powerful discharge of “ball capacitor” is very dangerous for human. Some other properties of BL are also discussing in this philosophical note. (shrink)

In eukaryotic cells the nucleus and its contents are separated from the cytoplasm by the nuclear envelope. Macromolecules, as well as smaller molecules and ions, can cross the nuclear envelope through the nuclear pore complex. Molecules greater than approx. 60 kDa and containing a nuclear localization signal are actively transported across the nuclear membranes, but there has been little evidence for regulatory mechanisms for smaller molecules and ions. Recently, diffusion across the nuclear envelope has been observed to be regulated by (...) nuclear cisternal Ca2+ concentrations. Following depletion of Ca2+ from the nuclear store by inositol 1,4,5‐trisphosphate or Ca2+ chelators, a fluorescent 10 kDa marker molecule was no longer able to enter the nucleus. Distinct conformational states of the nuclear pore complexes depended on the Ca2+ filling state of the nuclear envelope, supporting the assumption that a switch in the conformation of the nuclear pore complex may control the transport of intermediate‐sized molecules across the nuclear envelope. Thus nuclear Ca2+ stores may regulate the conformational state of the nuclear pore complex, and thereby passive diffusion of molecules between the cytosol and the nucleoplasm. The physiological significance of this finding is currently unknown. (shrink)

Kv10.1 is a voltage‐gated potassium channel relevant for tumor biology, but the underlying mechanism is still unclear. We propose that Kv10.1 plays a role coordinating primary cilium disassembly with cell cycle progression through localized changes of membrane potential at the ciliary base. Most non‐dividing cells display a primary cilium, an antenna‐like structure important for cell physiology. The cilium is disassembled when the cell divides, which requires an increase of Ca2+ concentration and a redistribution of phospholipids in its basal region, (...) both of which would be facilitated by local hyperpolarization. Cells lacking Kv10.1 show impaired ciliary disassembly and delayed entrance into mitosis. Kv10.1 is predominantly expressed during G2/M, a critical period for ciliary resorption, and localizes to the ciliary base and vesicles associated with the centrosome. This could explain the influence of Kv10.1 in cell proliferation, as well as phenotypic features of patients carrying gain of function mutations in the gene. (shrink)

As an artist I admittedly scrutinize all of the theories related to the arts closely. I do this for a number of reasons. The obvious one is that I have a deeply felt personal relationship with the subject matter. Less obvious is my experience in general. My early research was motivated by a desire to discover the historical circumstances that led to the difficulty in fitting visual art into the discussions I encountered. Generally, it seemed that the dominant framework trivialized (...) what I considered the most important aspects of the creative process. Over time I concluded that developing an interdisciplinary approach offered the best option for expanding views, although it is not an easy task. Establishing areas of commonality across a range of disciplines must somehow accommodate the ways in which each has developed a research agenda that seems to serve its core needs. In consciousness studies, for example, we have a field that relies heavily on scientific research and humanistic methodologies when building the philosophical models scholars use to structure theories. This methodology is not only removed from the nuts and bolts of art, it is also easily manipulated in discourse on art due to the ease with which we can fit aspects of art into the philosophical framework. Clearly this approach fits nicely with philosophically defined concepts such as meaning, emotion, and other elusive modes. In addition, using the well-honed categories aids in bracketing themes such as metaphor, interpretation, subjectivity, language and history. Nonetheless, in reading through the studies, I repeatedly conclude that the voices of practitioners need to be included to a greater degree. (shrink)

Ion Soteropoulos reconciles the contradiction between the finite and infinite and transforms this reconciliation into the founding principle of motion. This book will appeal to readers interested in the logical mechanics of the physical universe, the hidden powers of our finite brain, and the utility of robots in the future.