Globular protein hydration by a differential dielectrometric method]

A differential method is described for measuring dielectric constants and losses in aqueous protein solutions at millimetrerange wavelengths. Employment of the method allows to improve the accuracy of determining the degree of hydratation. A method has also been suggested for taking into account the contribution of ions to the dielectric constant of solutions. The differential method was used to study hydratation of nine globular proteins. The data obtained are compared with the corresponding values provided by other experimental techniques and with theoretical predictions based on some models of hydratation. Good agreement is obtained with results provided by the isopiestic and NMR techniques. The discrepancy shown for hemoglobin is discussed in the paper. As has been shown, the dielectric method registers a monomolecular surface layer of water only. With pH varying between 4.0 and 3.2, a significant increase is observed in the hydratation of serum albumin. Presumably, this effect is connected with a N--F conformational transition.     

Comparative study of the kinetics of the reduction of cytochrome c and the nitroxide radical in reversed aerosol OT micelles in octane

The comparison of the reduction kinetics of cytochrome c and nitroxide radical by ascorbate in reversed micelles of aerosol OT in octane was studied. The plot of the dependence of the reduction rate constant on the micelle hydratation is bell-shaped in the case of protein but shows the plateau form for the radical. The reaction rates decreases at high micelle concentrations. The equations have been drawn that connect the experimental rate constants with intramicellar biomolecular rate constant (km) for reagents unsolved in organic phase. In the case of strong hydratated micelles km for the radical reduction is practically equal to the rate constant in aqueous solution. For cytochrome c the ratio of these constants is less than 0.22, that may be explained by protein conformational changes detected by optical methods. For small micelle hydratation the dependence of the cytochrome reduction rate on ascorbate concentration is characterized by plateau. Under these conditions the limited stage of reaction is apparently the transition of the protein to the active conformation.     

Dependence of the inhibitory effect of metal cations on rat liver mitochondrial Ca2+ uptake on their physico-chemical properties

It has been found that Sr2+, La3+ Mn2+ (10-50 microM) inhibit Ca2+ transport into mitochondria in a competitive manner. Cd2+ ions show the mixed type inhibition of this transport. The inhibitory constants (Ki, microM) of the metals cations effect on Ca2+ transport increases in such a sequence: La3+ (2,11), Cd2+ (10,36), Mn2+ (49,29), Sr2+ (66,43). The metals cations inhibitory effect has an insignificant dependence on their ionic radii. But it is good correlated with the series of metals cations, based on the stability constants of their complexes with acetate (r = -0.96), aspartic (r = -0.91) and glutaminic acids and their hydratation enthalpy (r = -0.78). These data reveal that hydratation of metals cations and their interaction with carboxyles of Ca(2+)-uniporter plays an important role in the process of Ca2+ transport into mitochondrial matrix space and its inhibition by the metals cations. The mixed type inhibition of mitochondrial Ca2+ uptake by Cd2+ seems to be caused by the partial de-energization of mitochondria owing to Cd2+ interaction with SH-containing respiratory chain components and pore-forming ligands of mitochondrial membrane.     

Reactive changes in the capillaries of the mammillary bodies of the brains of aging animals

As electron microscopic investigation of the capillary wall in the mammillary bodies has demonstrated, in old animals the number of organells in the endothelial cells decreases; discomplexion and reduction of mitochondrial crists occur, their matrix becomes cleared; myelin-like structures are formed. In pericytes pigment inclusions are accumulating. Noncellular component of the basal layer loses its regular structure and foci of hydratation appear in it. When pharmacological loadings (adrenaline, aminazine) are applied to old animals, distrophic processes in the vascular wall increase; that results in disturbance of permeability, sharp hydratation of the basal layer, edema of the tissue elements around the brain and, hence, in a more prolonged restorative period.     

Diffusional attenuation of proton echo and control of changes in the cytoskeleton hydration level

Using the pulsed NMR-method with pulse gradient of the magnetic field, a study was made of changes in diffusional attenuation (DA) of proton echo in germs of triticum grains under the influence of agents depolymerizing cytoskeleton elements or inhibiting their ATP-activity. At a short diffusion time, we observed respective alterations of NMR-population in a fraction of cell water molecules contributing to DA at large values of pulse gradient. It is shown that the presence in DA of a site with essentially smaller coefficient of self-diffusion, as compared with basic cell water fraction, is not a consequence of restricted diffusion phenomenon. The observed changes in NMR-population of the appropriate fraction of cell water molecules are interpreted as changes in the level of cytoskeleton hydratation occurring under the influence of the used agents. A hypothesis is proposed for the functional role of similar changes in the level of hydratation of cytoskeleton elements located inside plamodesmata in the mechanism of plasmodesmatal water permeability regulation.     

The surface layer of the protein globule. Hydration of the alpha-chymotrypsin molecule]

The surface of the alpha-chymotrypsin globule is investigated using a three-dimensional model of the molecule, constructed on the basis of X-ray data by sectioning the space of the protein globule in cubic elements with a step of 3 A. The surface layer contains about 55% of the overall globule volume. The atomic density of so defined surface was found to be approximately equal to that in the inner part of the globule. Topographical maps of the alpha-chymotrypsin surface were drawn and an analysis of the distribution of polar and unpolar atoms and groups on the surface and in the inner part of the globule was carried out. Some conclusions drawn from the atomic density, energetic and structural heterogeneity of the surface and concerning the conformational integrity and functional activity of alpha-chymotrypsin molecule are presented. Some aspects of the protein hydration problem are discussed and a structural model of the alpha-chymotrypsin hydratation shell is proposed, the main features of which are amorphism and the lack of long-range effect on the structure of water around the hydrated protein globule.     

Hypothesis on the mechanism of cnidocyst discharge (author's transl)

The geometic aspects of the cnidocystic filament before invagination, during invagination and after the process of evagination are shown. Experiments are described that allow an approach to study the mechanism of discharge. It is suggested here that the filament is an elastic tube which, when it is intracapsular, is folded and spiraled and thus, under a constraining action. Evagination then consists simply in the release of the constraining force and reversion of the filament to the primitive cylindric shape. The presence of water seems indispensable to the process to take place; however this does not necessarily imply that a hydratation take place in the filament wall. It also seems obvious that if expansion is a normal tendency of the constrained filament, eversion is a result of the continuity between the wall of the filament and that of the capsule. In conclusion, the invagination of the tube during cnidogenesis may be interpreted as a mean of storing energy for the evagination.     

Evolution des acides amines libres intracellulaires

The influence of brackish waters on the isosmotic intracellular regulation has been studied on the abdominal muscle of Astacus leptodactylus. Parameters examined are hydratation and free amino acid concentration. Isosmotic intracellular regulation seems to be effective for this animal, some halophilous populations of which live in the Caspian Sea.     

Interferometric studies of the dynamics of hydration and dry matter content during light-dependent germination of the Anabaena variabilis Kützing akinetes]

Calculations following interference-microscopical measurements performed on akinetes (A), heterocyts (H), and "vegetative" cells (F) of the Cyanobacterium (blue-green alga) Anabaena variabilis resulted in significant higher values of mean absolute dry matter content of the akinetes (2.06 . 10(-10) g; as compared to 0.46 . 10(-10) g and 0.31 . 10(-10) g for H and F, respectively). tthe water content of these resting cells (63%) was significantly lower than in the other two types of cells (H: 85%, F: 77%). Light exposition of the akinetes in fresh nutrition medium (i. e., conditions allowing germination within 30--50 h) resulted in a decrease of the relative dry matter content so that already in the period preceding the outgrowth of the germling the water content of the vegetative cells was achieved. Simultaneously their volume increased by the uptake of water; whereas the absolute content of dry matter remained constant or was even temporarily diminished during the first period. Only in the second period the values increased in some cases and then remained constant up to germination. The increased dry matter content, however, was not a precondition necessary for the germination of the akinetes. In darkness under otherwise unaltered conditions the values remained unchanged or, after a light period, came back to the initial level. The results demonstrate that formation and germination of the resting cells of Cyanobacteria as well are connected with an alteration in the hydratation level, i. e., in cells which continuously are kept under water saturated conditions. This increase by hydratation during the germination period is, as the germination process itself, strictly controlled by light.     

The subunit structure of Pseudomonas cytochrome oxidase.

Pseudomonas cytochrome oxidase (EC 1.9.3.2) is composed of two subunits. Each subunit has a molecular weight of approx. 63000 and, according to the iron determination, contains two hemes. Cytochrome oxidase was subjected to various dissociation procedures to determine the stability of the dimeric structure. Progressive succinylation of 14 to 68% of the lysine residues of the enzyme increases the amount of the protein appearing in the subunit form (S20,W approximately 4 S) from 18 to 92%. At a high degree of succinylation a component with a sedimentation coefficient of approx. 2 S appears. The subunits with sedimentation coefficients of approx. 4 S and 2 S are also formed when the pH is below 4 or above 11. The same molecular weight (63000) was found for these two components in sodium dodecylsulphate electrophoresis. No dissociation of cytochrome oxidase was observed in salt solutions like 3 M NaC1 and 1 M Na2SO4, or in 6 M urea. The slight decrease in the sedimentation coefficients in NaC1 solutions is partly explained by preferential hydratation of the protein.     

In vivo analysis of the skin by Fourier-transformed infrared spectroscopy

Advantages of Fourier transform infrared spectroscopy using reflexion techniques are used for skin analyses. Several examples of spectra obtained with a skin analyser are given and the major absorptions in the range 3,500 to 1,150 cm-1 are assigned to fundamental vibrations. Some of them can be used to determine the hydratation level of the skin.     

The causes of hydration changes during DNA protonation

Changes of DNA hydration provoked by protonation in the way of Na+- and H+-ions exchange, and in the way of HCl addition to Na+-DNA, were analysed by IR-spectroscopy. Water is shown not to contribute essentially to the formation and stabilization of conformations arising when DNA is protonated. The differences between hydratation of DNA protonated by different ways are in the main accounted for by alteration of the quantities of Na+ and Cl- ions forming the aqueous-salt envelope of polynucleotide.     

X射线衍射法在研究蛋白质动态过程中的应用

介绍了X射线衍射技术在研究蛋白质动态过程中的应用.首先介绍了用常规X射线衍射法和劳埃X射线衍射法等数据采样法研究反应时间为几分钟的蛋白质催化反应.然后介绍了通过选择不匹配底物,不适宜酸度,选择温度和酸度的跳跃,金属和光化学瞬时激发达到反应的同步来研究反应时间为几秒钟的蛋白质催化反应.     

Distribution and roles of aquaporins in salivary glands

Salivary glands are involved in secretion of saliva, which is known to participate in the protection and hydratation of mucosal structures within the oral cavity, oropharynx and oesophagus, the initiation of digestion, some antimicrobial defence, and the protection from chemical and mechanical stress. Saliva secretion is a watery fluid containing electrolytes and a mixture of proteins and can be stimulated by muscarinic and adrenergic agonists. Since water movement is involved in saliva secretion, the expression, localization and function of aquaporins (AQPs) have been studied in salivary glands. This review will focus on the expression, localization and functional roles of the AQPs identified in salivary glands. The presence of AQP1, AQP5 and AQP8 has been generally accepted by many, while the presence of AQP3, AQP4, AQP6 and AQP7 still remains controversial. Functionally, AQP5 seems to be the only AQP thus far to be clearly playing a major role in the salivary secretion process. Modifications in AQPs expression and/or distribution have been reported in xerostomic conditions.