[Conformational stability of glutamate dehydrogenase and its complexes with specific ligands]. / Konformatsionnaia stabil'nost' glutamatdegidrogenazy i ee kompleksov so spetsificheskimi ligandami.

The isotermic denaturation of glutamatdehydrogenase (GDH) and its complexes with co-enzymes, substrates and allosteric regulators under the action of urea was studied. It was shown that the reaction of the enzyme with an allosteric inhibitor GTP is accompanied by a decrease in conformational stability of the catalytically active hexsamer GDH. Formation of a complex with the allosteric activator ADP increases the conformational stability of the enzyme. Studies on the isotermic unfolding of GDH in the presence of various phosphoric ethers of adenosine gave evidence that the stabilizing effect of ADP is based on the reaction of the enzyme with the adenine base of the regulator.

[Purification and some physico-chemical properties of glutamate dehydrogenase from beef brain]. / Ochistka glutamatdegidrogenazy iz mozga byka i ee nekotorye fiziko-khimicheskie svoistva.

A procedure for purification of glutamate dehydrogenase (GDH; L-glutamate NAD(P) oxidoreductase, EC 1.4.1.3) from beef brain has been developed. The enzyme preparation obtained has the specific activity of 6.7 units per mg of protein (192-fold enhance with a 30% yield of total activity of the homogenate). In some of its physico-chemical properties (pH optimum of catalyzed reactions, molecular weight, subunit structure, thermal stability) the brain GDH is identical to the enzyme from beef liver. The Km values for most of the coenzymes and substrates for the enzyme studied do not exceed those for beef liver enzyme more than 1,5--2-fold. The only exception is the Km value for glutamate, which in the case of brain GDH is 4 times less than that for the liver enzyme. The results obtained suggest that upon interaction with NAD the brain GDH reveals a relatively higher affinity for L-glutamate and L-ketoglutarate as compared to the liver enzyme.

[Heterogeneity and regulation of glutamate dehydrogenase activity in mammalian brain and liver]. / Geterogennost' i reguliatsiia aktivnosti glutamatdegidrogenazy v mozgu i pecheni mlekopitaiushchikh.

The present report concerns the study of the catalytic properties and the coenzyme affinity of glutamate dehydrogenase (GDH) and its isoenzymes in various preparations of the brain and liver as well as the different regulatory mechanisms controlling the ratio of the rates of biogenesis and breakdown of glutamate (Glu). The investigations carried out showed that GDH activity of various preparations of brain and liver (crystalline enzymes, cellular extracts and mitochondria) are markedly different from each other by their catalytic and regulatory properties as well as by their coenzyme activity. The data obtained make us conclude that nicotinamide-hypoxanthine-nucleotide (deaminoNAD) is a more effective coenzyme in the oxidative deamination of Glu, than other piridine nucleotides (NAD, NADP, deamino-NADP). It is supposed that in the formation of ammonia and amino acids in brain and especially liver, together with other known mechanisms an important role may be ascribed to the process of transdeamination. In this aspect, as a co-factor of oxidative deamination of Glu deamino-NAD (D-NAD) is thought to be of significant importance.

[Coenzyme specificity and isoenzyme spectrum of lactate dehydrogenase from different regions of the brain]. / Kofermentnaia spetsifichnost' i izofermentnyi nabor laktatdegidrogenazy razlichnykh otdelov mozga

The coenzyme affinity of lactate dehydrogenase of various parts of rat brain is different to deamino-NAD and NAD as well as to their reduced forms. In direct reactions NAD exhibits a higher activity than deamino-NAD. In the reverse reaction an opposite pattern is observed. The effect of deamino-NADH is much higher than that of NADH. Our studies have shown that the isoenzymes of LDH which are richer in H subunits have a higher affinity for deamino-NAD and deamino-NADH than for NAD and NADH. The isoenzymes of LDH that contain more M forms have opposite properties. LDH-3 does not show a pronounced selective affinity. The data obtained indicate that the activity of LDH and of its 5 isoenzymes varies greatly in different brain parts; crucial changes being observed in the relative percentage of molecular forms of LDH.

[Coenzyme specificity and isoenzyme spectrum of rat brain malate dehydrogenase]. / O kofermentnoi spetsifichnosti i izofermentnom spektre malatdegidrogenazy mozga krys

Our studies have shown that malatedehydrogenase of rat brain mitochondrial fraction (M-MDH) and soluble fraction (S-MDH) differ in respect to their coenzyme specificity. Affinity of both M-MDH and S-MDH to deamino-NAD (direct reaction) is about two times lower than toward NAD. In the reverse reaction deamino-NADH and NADH enhance the activity of M-MDH to the same extent while in the presence of deamino-NADH the activity of S-MDH is somewhat higher. The isoenzyme composition of M-MDH and S-MDH have been studied as well as the relative affinity of each isoenzyme towards deamino-NAD and NAD. Both M-MDH and S-MDH have been shown to consist of 3 isoenzymes, the second isoenzyme being the most active. The percentage of the 3-rd isoenzyme is the lowest. The coenzyme affinity of isoenzymes M-MDH and S-MDH have been shown to differ very markedly.