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Biomedical subjects

S D Varfolomeev

Publications and source records attributed to S D Varfolomeev.

At least 73 records · Page 4Linked to original sources
PubMed1985

[Are the regulatory cation-binding sites of opiate receptors a part of potential-dependent calcium channels of neuromembranes?].

Characteristics of 45Ca2+ transport into rat brain synaptosomes have been studied. The value of an equilibrium constant of the Ca2+ binding at a specific site of neuromembrane's potential-stimulated calcium channel was determined (KM = 0,27 +/- 0,04 mM). Stability constants of several metal-ion complexes with the cation-binding regulatory site at high- and low-affinity receptors for [D-Ala2, D-Leu5]enkephaline and morphine high-affinity receptors of rat brain membranes were estimated. Comparative analysis of the constants calculated along with the results of investigation of a calcium antagonist, Verapamil, and Zn2+ ions influence on various types of opiate receptors allow to conclude that regulatory cation-binding sites of enkephaline and morphine receptors are not identical to Ca2+-binding centres of potential-stimulated calcium channels of the neuromembrane.

Animals↗
PubMed1985

[The nature of cation-binding groups in binding sites for [[3H]Tyr1, D-Ala2, D-Leu5]enkephalin].

The influence of pH on binding of labeled stable analog of enkephalin, [3H]Tyr1, D-Ala2, D-Leu5]enkephalin, to high- and low-affinity receptors of rat brain membranes was studied. It was shown that alkali-earth metal ions combine with a deprotonated group (pKa 7,0) of the high-affinity receptor, thereby activating the latter. The effect of cations on the low-affinity enkephalin binding is independent of pH. The presence of phosphate group in the high-affinity binding site, as well as of imidazole residue in the low-affinity binding site was surmised. The latter supposition was supported by data on chemical modification of the membrane preparation with the aid of diethylpyrocarbonate.

Animals↗
PubMed1985

[Effect of external factors on the kinetic properties of PGH-synthase].

The influence of external factors, viz. reaction mixture temperature, presence of low- and high-molecular (tween-20) organic compounds, urea and the solution high ionic strength on kinetic properties of PGH synthetase has been studied. Some factors (high ionic strength, addition of organic compounds) were found to slow down irreversible inactivation of PGH synthetase in the course of the reaction. Sensitivity of the enzyme to the change of the solution ionic strength depends on environmental factors, rising on the microsomal enzyme solubilization with tween-20 and decreasing on further enhancement of the tween-20 concentration.

Animals↗
PubMed1985

[Radioreceptor analysis: the theoretical bases of the method].

General principles of radioreceptor assay pertinent to the membrane receptor preparations are discussed. The effects of the following factors are analyzed: concrete conditions of the assay, ligands affinity for receptors, the effects of relative contribution of nonspecific binding and ligands concentrations on the precision and sensitivity of the assay, as well as on the maximal measurable concentration found from a given standard curve and on the range of reliable concentrations for a compound under study. The performance of the assay is shown to be the better, the lower is the concentration of the labeled ligand, the higher its affinity for the receptor and the lower is the nonspecific binding contribution.

Binding, Competitive↗
PubMed1984

[Correlation between the property changes of opiate receptors and the structural integrity of synaptosomes].

The effect of incubation of rat brain synaptosomes at 37 degrees C isolated by the Hajos method, on parameters of high affinity opiate receptor binding of [3H]naloxone and the structural integrity of synaptosomes was studied. The structural integrity of synaptosomes was controlled by electron microscopy, by changes in lactate dehydrogenase activity as well as by the ability of synaptosomes to maintain the transmembrane potential, using the fluorescent probe 1-anilino-8-naphthalenesulfonate. It was found that during 60 min incubation, the structure of synaptosomes is considerably impaired. The dynamics of changes in the structural integrity of synaptosomes is correlated with the changes of parameters of naloxone binding to opiate receptors, which points to the dependence of synaptosomal receptors' properties on preparation nativity degree.

Anilino Naphthalenesulfonates↗
PubMed1984

[Stability of opiate receptors of wet and lyophilized preparations of rat brain membranes].

The effects of incubation of rat brain membranes at 0 degrees C on the specific binding of mu-ligands (naloxone, morphine) and the delta-ligand (D-Ala2, D-Leu5-enkephalin) to opiate receptors were studied. The effects of lyophilization of rat brain membranes on the properties of the opiate receptors were determined. The lyophilized brain membrane preparations revealed an extraordinarily high stability as compared to "wet" membranes. The experimental results suggest that morphine and D-Ala2, D-Leu5-enkephalin binding both to the high affinity and low affinity sites has different nature and point to the utility of stable and standard preparations of lyophilized membranes for the use in the receptor analysis of opiate and opioid peptides.

Animals↗
PubMed1984

[The effect of di- and trivalent metal ions on the binding of [3H-Tyr1, D-Ala2, D-Leu5] enkephalin to opiate receptors from the rat brain].

The influence of Ca2+, Mg2+, Mn2+, Sr2+, La3+, Nd3+, Sm3+, Eu3+, and Gd3+ ions on the binding of labeled, stable enkephalin analogue, [3H-Tyr1, D-Ala2, D-Leu5]enkephalin, to opiate receptors of the rat brain membrane preparations has been investigated. The formation of the complex can be described by a scheme involving at least two independent binding sites. The high affinity site does not discriminate the divalent and trivalent metal ions: all examined cations enhanced the enkephalin affinity for this site. The ligand binding to the low affinity site is potentiated only by Mn2+, Mg2+, and lathanoides. The maximal concentration of the binding sites of the above two types is not affected by the cations. The increase in the ionic strength of the solution entails a decrease in the affinity of the ligand for the high affinity binding site. It is shown that the effect of both di- and trivalent metal cations on the [3H-Tyr1, D-Ala2, D-Leu3] enkephalin binding is mediated through one cation attachment site on the respective enkephalin receptor.

Animals↗
PubMed1984

[The nature of functional groups regulating the catalytic activity of prostaglandin endoperoxide synthetase].

The influence of some reagents modifying NH2-, SH-groups or imidazole moiety, on the prostaglandin endoperoxide synthetase activity was studied. Acetaldehyde, pyridoxal phosphate, dithiobis (nitrobenzoic) acid and iodoacetamide were found not to affect the enzyme activity. The activity was abolished as a result of the interaction with p-chloromercuribenzoic acid and diethyl pyrocarbonate. The hemin completely protected the apo-enzyme against the inactivation with diethyl pyrocarbonate. The assumption about the presence of imidazole moiety in the active site of the enzyme was made.

Animals↗
PubMed1984

[Kinetic mechanisms of enzyme activity of the thromboxane synthetase system. Thromboxane synthetase of human platelets].

Partially purified preparations of prostaglandin endoperoxide-synthetase (PGH-synthetase) and thromboxane synthetase (PGH-convertase) were obtained from human platelets by ion exchange chromatography. The kinetics of prostaglandin H2 enzymatic conversion was studied in the presence of thromboxane synthetase from human platelets. It was found that prostaglandin H2 conversion into both thromboxane A2 and malonic dialdehyde is a catalytic process, i. e., its rate increases as the protein concentration rises. The linear dependence of the enzymatic reaction velocity on substrate concentration at a prostaglandin H2 concentrations below 10-15 microM was demonstrated. PGH-synthetase and PGH-convertase from human platelets exhibit similar enzymatic activity dependence on pH and temperature, PGH-convertase being more thermostable.

Blood Platelets↗
PubMed1984

[Synthesis of thromboxane A2: limiting stages of primary thrombocyte aggregation in humans initiated by arachidonic acid and its metabolic products].

A photocolorimetric method has been employed for kinetic investigation of aggregation of human platelets under the effects of arachidonic acid (AA) and the products of its metabolism in the platelets. The platelet aggregation was induced by AA and prostaglandin (PG)H2, the precursors of thromboxane (Tx). The initial rate of aggregation depended on AA and PGH2, concentrations. The nature of the influence of selective inhibitors of PGH-synthetase (indomethacin) and PGH-convertase (imidazole) on the rate of aggregation is suggestive of the rate-limiting type of enzymatic reactions of AA conversion into TxA2. Addition to the platelet suspension of solubilized PGH-convertase accelerates the PGH2-induced aggregation. Analysis of platelet aggregation processes induced by AA and PGH2 demonstrated that the enzymatic synthesis of TxA2 is one of the rate-limiting steps within the framework of molecular modifications responsible for the platelet aggregate formation.

Arachidonic Acids↗
PubMed1984

[Enzyme inactivation in the reaction process. Regulatory role].

Some peculiarities of regulation of the enzymatic reaction involving enzyme inactivation in an open system were studied. The steady- and non-steady-state behaviour of the system upon the perturbing influence of various substrate concentrations was investigated. The steady-state responses of the system involving enzyme inactivation in the course of the reaction were compared to those for the known mechanisms directed at stabilization of the product concentration, such as competitive and incompetitive allosteric inhibition and enzyme inactivation by the reaction product. Two unique properties of the open system involving the enzyme inactivation in the course of the reaction were revealed: (1) The system is capable of maintaining an absolutely constant level of steady-state concentration of the reaction product at variable steady-state concentration of the substrate. (2) At high perturbing deviations of substrate concentrations, the non-steady response of equal amplitude is evoked; the amplitude of deviations in the product concentrations ceases to depend on the deviations in the substrate concentration. The role of regulatory influences in the mechanisms of synthesis and the effects of prostaglandins, essential regulators of the majority of physiological functions, are discussed.

Allosteric Regulation↗
PubMed1983

[Kinetics of prostaglandin H2 degradation. A method of determining prostaglandin H-convertase activity].

The quantitative study of the processes that accompany nonenzymatic degradation of prostaglandin H2 has been carried out. The thiobarbituric acid test which shows the content of malonic dialdehyde in the reaction mixture has been used to study kinetics of the degradation. The apparent rate constants of this process have been pH-independent over the pH-range 5,5-9,5, and the calculated conversion halftime changes from 5,8 to 3,6 min at these pH values. Thromboxane synthetase from human platelets has been chosen to demonstrate the possibility of application of thiobarbituric acid test for determination of the activity of prostaglandin endoperoxide convertase. It has been shown that the apparent rate constant of the reaction in the presence of the enzyme is the linear function of its concentration.

Chemical Phenomena↗
PubMed1983

[Effect of the modification of carboxylic groups in protohemin IX on the properties of endoperoxide prostaglandin synthetase].

The effect of protohemin IX and its modified analogs (monomethyl ester, dimethyl ester, as well as monoamides with Val-Phe-OCH3 or Leu-His-OCH3) has been examined on the activity of prostaglandin endoperoxide synthetase from sheep vesicular glands (PGH-synthetase, EC 1.14.99.1, isolated as apoenzyme). For holoenzymes having the above compounds as prosthetic groups, the dissociation constants, relative activities and the apparent inactivation constants in the course of the reaction have been determined. The effect of Tween 20 on the indicated parameters for holoenzymes with protohemin IX and its mono- and dimethyl esters has been studied. Modification of one of the two carboxylic groups of protohemin IX markedly increases the dissociation constant for the respective holoenzyme and virtually does not affect catalytic activity. Modification of both carboxylic groups of protohemin IX hinder the binding with the apoenzyme and strongly reduces the catalytic activity of the holoenzyme.

Animals↗
PubMed1983

[Effect of opiates on Ca2+ transport in synaptosomes].

Potassium-stimulated uptake of Ca2+ by nerve-ending fractions from rat brain (synaptosomes) is inhibited by morphine and [D-Ala2, D-Leu5]enkephalin. This effect develops significantly within 1 minute. The opiates do not affect the Ca2+ efflux from the synaptosomes. Naloxone, the opiate antagonist, does not reverse the effect of morphine on synaptosomal Ca2+ uptake, and in this respect itself acts similarly to morphine).

Animals↗
PubMed1982

[Endoperoxide prostaglandin synthetase from the microsomal fraction of human platelets].

The reaction of oxidation of arachidonic acid by the enzymes localized in the microsomal fraction of human platelet was investigated. It was shown that the preparations of washed microsomes are devoid of the lipoxygenase activity but possess the endoperoxideprostaglandin synthetase activity. The oxidation of arachidonic acid is a three substrates process, whose indispensable component is a reducing agent, i. e. an electron donor. The stoichiometry of the three substrates reaction as well as the dependence of the reaction rate on the concentration of O2, arachidonic acid and the electron donor, haemin were studied. The effective values of some reaction parameters were determined.

Arachidonic Acid↗