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O D Lopina

Publications and source records attributed to O D Lopina.

At least 19 recordsLinked to original sources
PubMed1995

Characterization of the subunit isoforms of duck salt gland Na/K adenosine triphosphatase.

The N-terminal sequences of the alpha and beta subunits from the Na/K-ATPase of duck salt gland have been determined by automated Edman degradation chemistry. These sequences were compared to sequences previously reported for Na/K-ATPase subunits from other sources in order to determine the subunit isoform composition of the salt gland enzyme. The comparisons indicate that the duck salt gland enzyme is composed of an alpha-1 subunit and a beta-1 subunit. This subunit isoform composition is consistent with the involvement of this enzyme in sodium excretion as Na/K-ATPases in other tissues involved in sodium excretion also have this subunit isoform composition.

Amino Acid Sequence↗
PubMed1995

A comparative study of Na+/K(+)-ATPases of duck salt gland and canine kidney: implications for the enzyme's reaction mechanism.

Highly purified preparations of duck salt gland and canine kidney Na+/K(+)-ATPases with comparable specific activities were used to clarify the causes of previously reported differences between the substrate-velocity curves of these enzymes. When assays were done under identical conditions (pH 7.4; 37 degrees C), and a wide range of closely spaced ATP concentrations were used, the curves of both enzymes exhibited intermediary plateaus, as noted before for the salt gland enzyme. The two enzymes also had the same numbers of phosphorylation and ouabain binding sites, and their catalytic subunits were of the alpha 1 isoform type as revealed by immunostaining with specific antibodies. The findings suggest that the substrate-velocity curves of all widely used Na+/K(+)-ATPases may contain an intermediary plateau which is diagnostic of reaction mechanisms that generate rate equations containing powers of substrate concentration greater than two, e.g., a mechanism involving an oligomer with more than two protomers.

Animals↗
PubMed1995

[Effect of ligands on rotational mobility of Na,K-ATPase].

Phosphorescence anisotropy of eosin-5'-isothiocyanate labelled Na,K-ATPase purified from duck salt glands has been studied. The initial anisotropy value is 0.235 +/- 0.015 (room temperature) and does not depend on the enzyme conformation (sodium or potassium). The experimental curve is fitted into a two-exponential curve with residual term, the fast component corresponds to the rotational mobility of the functional unit of Na,K-ATPase (promoter), while the slow one--to that of larger associates. In the presence of ligands modifying the conformational state of Na,K-ATPase (sodium, potassium, ATP) the rotational mobility of the fast component does not change in contrast with the slow one. A comparison of the enzyme rotational mobility in the presence of ligands simulating different steps of hydrolytic cycle suggests that interprotomer interactions are changed in the course of hydrolytic cycle: the fraction of larger associates increases at the step of the enzyme interactions with potassium ions, whereas their mobility in the bilayer enhances sharply after interaction with ATP. In the presence of the 2% non-ionic detergent, C12E9, the initial anisotropy value decreases down to 0.1; the residual term disappears thereby, while the curve is still two-exponential. However, the difference in the rotational mobility of sodium and potassium conformers diminishes. At the same time, the ratios between protomers and oligomers in the presence of sodium and potassium become approximated. This indicates that in the presence of the detergent high molecular weight associates are solubilized, the mobility of the both protomers and oligomers of Na,K-ATPase increases, while the difference between the mobilities of sodium and potassium conformers is disappeared.

Animals↗
PubMed1994

[Rotational mobility of membrane-bound Na,K-ATPase].

The rotational mobility of E1 and E2 conformers of duck salt gland Na,K-ATPase labelled with eosine-5'-isothiocyanate (EITC) was studied using a time-resolved phosphorescence anisotropy approach. For each conformer, two types of the rotational mobility were found. The rotational correlation time of the faster component equal to about 15 microseconds at 20 degrees for the both conformers, was ascribed to the rotation of the (alpha beta) protomer with an apparent radius 2.4 nm. The slower component (100-500 microseconds depending on experimental conditions) was suggested to reflect the presence in the bilayer of associates between Na,K-ATPase molecules or those with other protein constituents of the membrane bilayer. A rise in temperature tends to decrease the fast component with a subsequent increase in the slow component of the experimental curve, apparently due to oligomerisation of the protomers into oligomers. The size of the oligomers depends on pH and temperature and under favourable conditions may come up to octamers.

Animals↗
PubMed1991

The mechanism of the modifying effect of ATP on Na(+)-K+ ATPase.

On the basis of a review of the literature and a study of the molecular and kinetic properties of Na(+)-K+ ATPase, a model is proposed that explains the regulation of the activity of the enzyme by ATP in terms of an acceleration of the E2----E1 transition. It is presumed that the transition occurs via a short-lived oligomer whose formation is accelerated by ATP. In the context of this model, the non-Michaelis-Menton kinetics of the enzyme can be explained by interprotomer interactions. After solubilization of the enzyme with octaethylene glycol dodecyl ether, the hydrolysis of ATP follows ordinary Michaelis-Menton kinetics. The validity of the model is also supported by radiation-inactivation experiments with a nucleotide (GTP) which does not accelerate the E2----E1 transition, as well as by experiments with a low concentration of ATP. In both situations, the size of the molecular target corresponds to the monomeric form of the enzyme.

Adenosine Triphosphate↗
PubMed1990

Na,K-ATPase labelled with 5-iodoacetamidofluorescein: E2-E1 conformational transition induced by different nucleotides.

A conformational transition between E2 and E1 forms of Na, K-ATPase induced by different nucleotides has been studied under steady state conditions using the enzyme labelled with 5-iodoacetamidofluorescein. In the presence of K+ the plot of fluorescence as a function of [ATP], [ADP] or [CTP] (in a range of 5 microM-12 mM) is a biphasic one. A similar dependence for AMP, ITP, GTP and UTP demonstrates a hyperbolic behaviour. The data suggest that the shift in the equilibrium between E2 and E1 forms of Na,K-ATPase towards the E1 conformation is induced by ATP binding both with high and low affinity sites. Two structural features of ATP are apparently important for its interaction with more than one type of ATP binding sites or for providing for E2-E1 transition induced by this interaction: (i) beta-phosphate group in the terminal part of the molecule, (ii) unprotonated N1 and/or NH2-group in the 6th position of the purine base.

Adenosine Triphosphate↗
PubMed1990

The biochemical characteristics of stress-sensitive hypertensive rats.

The biological characteristics of a line of stress-sensitive hypertensive (SSH) rats genetically selected from Wistar rats are described, in particular the dynamics of arterial blood pressure and the biochemical properties of the Na(+)-K+ ATPase present in the outer renal medulla. Changes in the specific activity of this enzyme are discussed in terms of the lipid composition of the membrane bilayer and the amount of endogenous ouabain-like compounds present in the blood of the animals under study. Rats of both strains, Wistar and SSH, were studied under conditions of rest and stress (8 day regime of daily 30 min immobilization). The production in vivo of adrenal mineralocorticoids and glucocorticoids is estimated and several biochemical features of the pathogenesis of essential hypertension are discussed.

Adrenal Cortex Hormones↗
PubMed1990

In vivo corticosteroid production by the adrenal glands of the SSH (stress-sensitive hypertensive) strain of rat.

The corticosteroid hormonal status of a line of stress-sensitive hypertensive (SSH) rats genetically selected from normotensive Wistar rats was characterized. The secretion of mineralocorticoids and glucocorticoids by the adrenal glands was measured in vivo under control conditions, after immobilization stress, and after stress in the presence of perorally administered androsol acetate, a potential antihypertensive agent. Eleven corticosteroids were detected, six of which were identified. The SSH rat line is characterized by an increased level of glucocorticoids (corticosterone and cortisone) compared to that seen in normotensive Wistar rats, under both normal and stress conditions. The secretion of individual corticosteroids under conditions of stress and steroid treatment changed to different extents in control and hypertensive rats. It is suggested that the ratios of the different classes of corticosteroids (glucocorticoid to mineralocorticoid), rather than the concentrations of the individual hormones, be used in assessing the effects of substances on the pathogenesis of idiopathic hypertension. Androsol acetate 'normalized' the reaction of the adrenocortical system in response to stress in SSH rats.

Adrenal Cortex↗
PubMed1990

Na,K-ATPase: radiation inactivation studies.

Na,K-ATPase from duck salt gland and ox brain in the membrane-bound or solubilized form was studied by the radiation inactivation technique using ATP, CTP, GTP or p-NPP as substrates. The values of radiation inactivation size (RIS) were compared with the target size (TS) for the alpha-subunit of the enzyme obtained by an independent method as well as with analytical centrifugation data obtained for C12E8-solubilized enzyme. It was concluded that during ATP (CTP) hydrolysis the enzyme operates as an oligomeric structure; the complex formation requires the presence of K+ and adenosine triphosphate binding to the sites with a low affinity for the nucleotide. Specially designed experiments revealed that the degree of enzyme oligomerization increases with an increase in the microviscosity of the membrane lipid environment.

Adenosine Triphosphate↗
PubMed1990

[The regulation of Na, K-ATPase activity by the substrate].

The mechanism of functioning of Na, K-ATPase system is considered, the peculiarities of hydrolysis in different substrates are described. The experimental results testify to the role of substrate structure in E2----E1-transition, Na+ transport, K(+)-dependent phosphatase activity and quaternary structure of enzyme. The regulatory role of molecular organization of Na, K-ATPase in ion transport is discussed.

Adenosine Triphosphate↗
PubMed1990

[The in vivo production of corticosteroids by the adrenals in rats of the SSHR hypertensive strain].

The review contains the hormonal characteristic of the line of stress sensitive hypertensive rats (SSHR) developed from normotensive Wistar rats (WR) during genetic selection. The in vivo production mineralo- and glucocorticoids by rat adrenal glands is estimated. It is shown that SSHR have an increased level of glucocorticoids. The biochemical features of pathogenesis of essential hypertension are discussed.

Adrenal Cortex Hormones↗
PubMed1989

A biochemical approach to essential hypertension.

Using multivariate statistical analysis, an attempt has been made to select hypertensive and normotensive sub-groups of subjects on the basis of certain parameters of their blood serum, such as the inhibition of purified Na,K-ATPase by serum and the content of two proteins with molecular masses of 12 and 15 kDa. An analysis of 20 human beings (10 hypertensive and 10 normotensive individuals) revealed that the best division into sub-groups is achieved only through the use of a combination of these three parameters.

Adolescent↗
PubMed1989

[The role of the substrate structure in the function of Na,K-ATPase].

The mechanism of Na,K-ATPase function is reviewed. The peculiarities of hydrolysis of various substrates are described. The experimental results testify to the effect of substrate structure on the E2----E1 transition, rate of Na+ transport, K-dependent phosphatase activation and the quaternary structure of Na,K-ATPase. A conclusion is drawn that the proton-acceptor properties of the substrate play a role in the regulation of ion transport by Na,K-ATPase.

Chemical Phenomena↗
PubMed1984

Na,K-dependent adenosine triphosphate phosphohydrolase: activation of the phosphatase reaction by ATP analogs.

The effect of N1-substituted analogs of ATP on the hydrolysis of umbelliferone phosphate by Na,K-ATPase has demonstrated: analogs having a negatively charged substituent (N1-oxy- or N1-carbo-methoxy-ATP) and capable of accepting H+ induce an activation similar to that of ATP; N1-methoxy-ATP, containing an uncharged substituent, does not affect the phosphatase reaction at low concentration and inhibits it at higher concentration. It has been assumed that ATP binding to Na,K-ATPase induces formation of a hydrogen bond between the nitrogen atom at the first position of the purine base and appropriate amino acid of active centre, with a subsequent attachment of H+ to ATP, thus facilitating the transition of Na,K-ATPase from the K+- to the Na+-form.

Adenosine Triphosphate↗
PubMed1984

Diphenylhexatriene and pyrene as tools for characterization of biological membranes.

The temperature behaviour of the fluorescent probes--1,6- diphenyl-1,3,5-hexatriene (DPH) and pyrene--in the outer and intracellular membranes differs markedly. Fluorescence polarization of DPH in microsomal preparations of duck salt gland and bovine brain enriched with Na,K-ATPase decreases nonmonotonously with an increase in temperature, the critical temperature being coincident with that for Na,K-ATPase. In preparations of sarcoplasmic reticulum intracellular membranes enriched with Ca-ATPase, the DPH fluorescence polarization changes linearly with temperature. Studies of the lipid composition of membrane preparations demonstrated that intracellular membranes are more fluid than outer plasma membranes. At the same time, these membranes reveal a critical temperature for another parameter that characterizes the changes in the hydrophobic volume of the bilayer, i.e., the degree of pyrene excimerization. The Arrhenius plots for this reaction coincide with that for Ca-ATPase in the same preparations.

Animals↗