[Effect of thiol reagents on cerebral glutaminase activity].

Abstract

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.