[Effect of mineralocorticoid analogs on Na(+),K(+)-dependent ATPase]. / Vliianie analogov mineralokortikoidov na Na(+),K(+)-zavisimuiu ATP-azu.

The effect of 42 steroids of the 20-ketopregnane series with heterocycles fused in positions 16 alpha and 17 alpha on the activity of Na+,K(+)-activated ATPase from pig kidney was studied. It was shown that the studied compounds could be divided into two groups. The compounds from the first group stimulate the ATPase at low concentrations (1 x 10(-8)-1 x 10(-7) M) and inhibit it at high concentrations (1 x 10(-4) M). The second group of compounds stimulated the sodium pump at either concentration. This is explained by the cooperative action of the ATPase tetramer: after the reaction of its first binding site with the ligand, the tetramer changes the conformation and specificity of its other binding sites. Computer analysis of this series of compounds was carried out and a mathematical model of the dependence of their activities on the structure of their substituents was obtained with a high correlation coefficient and a satisfactory predictive power. This confirmed the structural similarity of the studied compounds with respect to their interaction with the ATPase binding sites. The method of descriptor analysis that was applied in this study is a new variant of approximation; it is based on the use of symbol variables as descriptors.

Structural basis of steroid compounds interaction with "digitalis"-receptor sites of Na,K-dependent ATPase.

Twenty-two Steroid molecules have been tested for the inhibition Na,K-dependent ATPase at 10(-7)-10(-4) M concentrations. At the 10(-5) M concentration of the investigated molecules, inhibition ranged from 8 to 36%. To explain the structure-inhibition % relationship, we determined the value of heteropolarity or biphilicity moment of these molecules. This value would appear to be dependent on the space location and hydrophilicity of the molecule elementary fragments, and to the degree of their water accessibility; however, it is independent of the hydrophilicity of the molecules as a whole. On the basis of the obtained data, details of Na,K-ATPase digitalis-receptor structure and the mechanism of the glycoside-receptor interaction are discussed.

Ion-transporting properties and ATPase activity of (Na+ + K+)-ATPase large subunit incorporated into bilayer lipid membranes.

A purified (Na+ + K+)-ATPase large subunit obtained from microsomes by water-alcohol extraction was incorporated into a bilayer lipid membrane. The protein formed in the membrane conductance channels which were sensitive to ouabain and selective for monovalent cations. ATP activated these channels in the presence of sodium and potassium ions. When sodium ions were eliminated ATP did not change the conductance of the modified membrane whereas p-nitrophenyl phosphate increased it. The (Na+ + K+)-ATPase large subunit incorporated into bilayer lipid membrane possessed an ATPase activity. The presence of a potential on the membrane was a necessary condition for the enzyme incorporated into a bilayer lipid membrane to show high ATPase activity. Increasing the potential above 100 mV resulted in the closing of conductance channels.

[Mechanism of Na,K-ATPase inhibition with gossypol and megasin]. / Izuchenie mekhanizma ingibirovaniia Na,K-ATFazy gossipolom i megosinom.

Kinetic patterns of megosin and gossypol effects on properties of highly purified Na+, K+-ATPase were studied. Inhibition of the enzymatic activity appears to occur due to interaction of these compounds with the enzyme probound to the intracellular side of the transport enzyme.

[Ion channels formed in bilayer lipid membranes by large subunits of Na,K-ATPase and activated by ATP and p-nitrophenylphosphate]. / Ionnye kanaly, obrazuemye v bisloinykh lipidnykh membranakh bol'shimi sub''edinitsami Na,K-ATFazy i aktiviruemye ATF i p-nitrofenilfosfatom.

BLM modified by a large subunit of Na,K-ATPase is capable of forming ATP-dependent channels of conductivity in the presence of Na+ and K+ ions from the reaction medium eliminated the ATP effect, however, in this case the pNPP activated K+-conductivity is observed.

[Effect of small doses of gamma radiation on the activity of marker enzymes in the plasma membranes of chick embryo liver]. / Deistvie malykh doz gamma-oblucheniia na aktivnost' markernykh fermentov plazmaticheskikh membran pecheni émbrionov kur.

A study was made of marker enzyme activity in plasma membranes of chick liver during embryogenesis in normal conditions and after exposure to ionizing radiation. It was shown that irradiation with small doses of eggs prior to incubation and of chick embryos during different periods of the prenatal ontogenesis caused essential changes in activity of membrane-bound enzymes of liver plasmolemma. Stimulation with small radiation doses was most effective with preincubation irradiation of eggs and most manifest at later stages of the prenatal ontogenesis. Thus, the marker enzymes were shown to play a significant role in the realization of the stimulatory effect of low-level radiation.

[The effect of the distribution of polar groups in a steroid molecule on its inhibition of Na+,K+-ATPase]. / Vliianie raspredeleniia poliarnykh grupp v molekule steroida na ego ingibiruiushchee deistvie na Na+,K+-ATPazu.

Transformed steroids having oxidized side chains in the D ring site and varying by polarity of the substituent at the ring A C(3)-position--acetates, glucosides or with free hydroxyls--in the concentration range 1 X 10(-4) - 1 X 10(-7) M were found to inhibit Na+, K+-ATPase. The extent of inhibition decreases with the rise in the polarity of the A region of the steroid molecule. With the compound devoid of polar groups in the D region an increase in the inhibitory activity is observed on passing from 3-acetate to 3-glucoside. The data obtained confirm the relationship between the extent of Na+, K+-ATPase inhibition and biphilicity of the molecule.

[Molecular polarity dependence of the transformed steroid effect on Na,K-ATPase]. / Zavisimost' vliianiia transformirovannykh steroidov na Na,K-ATPazy ot bifil'nosti ikh molekul.

The transformed steroids containing an additional cycle E (delta-lactone or 16.23-pyranone) or 23-carbethoxy side chain (1.10(-5) M) inhibit Na,K-ATPase from pig kidney medulla. The steroid structure has a noticeable effect on ATPase inhibiton varying from 9 to 35%. The data obtained suggest that the position, stereochemistry and the uneven distribution of polar substituents in the steroid molecule are essential for ATPase inhibition by steroid aglycons.

[Effect of transformed steroids on Na,K-dependent ATPase]. / Vliianie transformirovannykh steroidov na Na,K-zavisimuiu ATPazy.

The transformed steroids containing delta 5-3 beta-hydroxy- or 3 beta, 5 alpha-dihydroxy-6-keto groups in the A/B rings and an additional cycle E (17,20-dihydroxy-delta-lactone, 16,23-pyranone or delta 20(22)-16 alpha, 17 alpha-dihydroxy-23-carbethoxy-side chain) (1 . 10(-5) M) inhibit Na+,K+-ATPase from pig kidney medulla or from ox brain. The steroid structure has a noticeable effect on ATPase inhibition varying from 3 to 26%. The data obtained suggest that the uneven distribution of polar substituents in the steroid molecule is essential for ATPase inhibition by steroid aglycons.

[Channel-forming protein from a Na, K-ATPase preparation from porcine renal medulla]. / Kanaloobrazuiushchii belok iz preparata Na, K-ATFazy mozgovogo sloia pochek svin'i.

Protein inducing formation of the monovalent cation selective channels on bilayer lipid membrane (BLM) was isolated by ethanol extraction from the great subunits of Na+, K+ ATPase or pork kidney microsomes. Conductance of the single channels in the presence of 2 microgram/ml of protein, 0.016 A KC1 and 0.08 M NaCl is equal to 40 p. The membrane potential of a ten-fold potassium ion gradient is close to a theoretical one. Ouabain (5 X 10(-5) M-1 X 10(4) M) inhibits the formation of the channels. KCl (0.03-0.08 M) eliminates the ouabain effect.

[Interaction of Na,K-ATPase with modifying ATP analogs and chloromethylphosphonic acid]. / Vzaimodeistvie Na,K-ATPazy s modifitsiruiushchimi analogami ATP i khlormetilfosfonovoi kislotoi.

The interaction of synthetic ATP analogs, containing active groups in the triphosphate moiety and in the 8-position of the nucleotide molecule, with highly purified Na, K-ATPase from the medullar layer of porcine kidney was studied. It was found that 11 out of 17 ATP analogs studied irreversibly inhibit the ATPase activity of the enzyme. The pH optimum of the enzyme inactivation by adenosine-5'-(beta-chloroethylphosphate) and adenosine-5'-(p-fluorosulfonylphenylphosphate) beside the pronounced protective effect of ATP suggests possible covalent blocking of histidine and dicarboxylic amino acid residues in the enzyme active center. The irreversible inhibition of the enzyme by "oxo-ATP" containing aldehyde groups in the modified ribose residue in the presence of sodium borohydride suggests a possible presence of the lysine residue epsilon-amino group in the ATP binding site of the enzyme. Na, K-ATPase was found to possess an inorganic phosphate binding site, which is specifically blocked by chloromethylphosphonic acid. the accessibility of this site for modification depends on ATP, NA+ and K+.

[Stabilization of Na+, K+-adenosine triphosphatase by dimethyl sulfoxide under inactivation by urea]. / Stabilizatsiia Na+, K+-adenozintrifosfatazy dimetilsul'foksidom pri inaktivatsii mochevinoi.

Hydrophobic agents, e.g. methanol, ethanol, isopropanol, acetone and dioxane were shown to induce irreversible inactivation of Na+, K+-adenosine triphosphatase beginning with their concentrations of 20 to 35%, whereas dimethyl sulphoxide exerted similar effect only at concentration of 50% and higher. Urea also irreversibly inactivated Na+, K+-adenosine triphosphatase, beginning with a concentration of about 20%. It was found that, dimethyl sulphoxide contrary to the other hydrophobic agents studied, protected Na+, K+-adenosine triphosphatase against the inactivating (denaturing) action of urea. The highest stabilizing effect of dimethyl sulphoxide was displayed at concentrations from 20 to 30%.

[Binding of Rb86 by a microsomal fraction of bovine cerebral cortex cells]. / Sviazyvanie Rb86 mikrosomal'noi fraktsiei kletok kory mozga byka

The maximal binding of 86Rb was noted when ions of Mg, ATP and Na were present simultaneously. The availability of olytoriside (1-10(-4)M), CaCl2 (1-10(-3)M) and phospholipase A (1-10(-5)M) in the medium and the removal of Na and substitution of ATP for ADP decreased to a different extent the binding of 86Rb.

[Tryptophan fluorescence of Na+,K+-ATPase preparations]. / Issledovanie triptofanovoi fluorestsentsii preparatov Na+, K+-ATFazy

On the strength of the study of tryptophan fluorescence of Na+, K+-ATPase preparation a conclusion about conformational changes of the enzume molecule at the level of its tertiary structure is made. The largest changes of intensity and position of fluorescence spectrum consequently the macromolecule structure are discovered at the formation of Mg-ATP-enzyme complex.

[Role of calcium ions and fatty acids in the inhibition of Mg2+, Na+ and K+-ATPases by means of the "direct" hemolysin and phospholipase A of cobra venom]. / Uchastie ionov kal'tsiia i zhirnykh kislot v tormozhenii Mg2+ i Na+, K+-ATFaz "priamym" gemolizinom i fosfolipazoi a iada kobry

The influence of calcium ions and fatty acids in the action of direct hemolytic factor and phospholipase A on Mg2+ and Na+, K+-ATPases was investigated. It was established that calcium activates greatly phospholipase A and to a less extent--the direct hemolytic factor. The activity of ATPases is inhibited most effectively by the system consisting of phospholipase A, direct hemolytic factor and Ca2+. Fatty acids can participate in the mechanism of membrane ATPases inhibition.