Desensitization of the allosteric sites of glutamate dehydrogenase by fluorodinitrobenzene

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Abstract

Beef liver glutamate dehydrogenase has been reported to possess several kinds of binding sites: a) substrate or active site for NAD, NADH2, NADP and NADPH2, b) purine nucleotide site, c) non-substrate site which binds only NADH2(Frieden, 1963). The availability of site b) is of considerable interest, in view of the possibility of control of reaction rates by purine nucleotides invivo. Under certain conditions, some of these nucleotides (e.g. ADP) enhance, and other (e.g. GTP) inhibit, the enzymatically catalyzed reaction. Kinetic studies have shown that purine nucleotides compete for the same site and that relatively high concentrations of oxidized pyridine nucleotides give unexpectedly high reaction rates. This activation has been as cribed to interaction at the purine nucleotide site (Olson and Anfinsen, 1953; Frieden, 1959a; di Prisco etal., 1965).

This paper deals with the modifications of the first two kinds of enzymatic sites caused by treating the enzyme with fluorodinitrobenzene, a compound known to react with functional groups present in proteins. Evidence is provided for the existence of separate ADP- and GTP-binding sites; the evidence indicates also that the sites of interaction for “activating” concentrations of NAD are identical to the GTP sites.

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