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V S Oganesian

Publications and source records attributed to V S Oganesian.

4 recordsLinked to original sources
PubMed1975

[Effect of glutamic acid on the interrelationship of the effects of different activators of cerebral glutaminase].

When phosphate and tyroxine (activators of brain glutaminase) are used in small amounts, a potentiation of their stimulatory effect is observed. Higher concentrations exhibit an opposite effect. Glutamic acid has a strong inhibitory effect on all the activators of glutaminase given separately. The inhibitory effect of glutamate increases on lowering the pH. On the other hand the potentiation observed on adding two stimulators is increased greatly in the presence of glutamate. On the addition of tyroxine to other stimulators a greater potentiation and rise of glutaminase activity are observed. The potentiation, which occurs on the joint addition of phosphate and tyroxine, is raised with the increase of the amount of glutamic acid, while on the contrary on joining phosphate with other stimulators potentiation is reduced. Potentiation is variable and depends on the pH. Preincubation of brain mitochondrial fraction with guanidine chloride inhibits markedly the stimulatory effect of all the stimulators used, but their joint addition almost abolishes the potentiating effect. In the presence of glutamic acid, due to the increase of the cooperative effect between the two stimulators, glutaminase activity is greatly increased and sometimes its inhibitory effect is not even observed. The data obtained indicate that in brain glutamic acid in the presence of phosphate+thyroxine cannot be considered as an inhibitor of glutaminase and that the important factor here is not so much the absolute levels of the activators as their favorable combinations.

Animals↗
PubMed1974

[Effect of thiol reagents on cerebral glutaminase activity].

It has been shown that the glutaminase activity of brain mitochondrial fractions, which is stimulated by various activators, is completely abolished on 10 min preincubation with parachlormercurybenzoate, 5,5'-dithiobis-(2-nitrobenzoate), N-ethylmaleimide, iodoacetamid, CdCl2, ZnCl2 and CuCl2. With the purpose of elucidating the role of SH-groups in glutaminase activity we have studied the possibilities of preventing loss of enzyme activity by substrates and activators. We have shown that glutamine is effective only in the case of CuCl2. It should be noted that preincubation of brain mitochondrial fractions with activators greatly reduces the inhibitory effects of thiol reagents. Besides, activators differ in their effect in preventing glutaminase inactivation by various SH-reagents. After preincubation of glutaminase with activators their protective effect depends on whether glutamin is added together with the inhibitor or after some time. In one case their protective effect increases, in the other decreases and in the third case remains unchanged. On the basis of the data obtained the authors conclude that SH groups of brain glutaminase are not present in the active center and have an important functional significance for its catalytic active conformation.

Animals↗