Summary: has two chromatographically distinct forms of glutamate dehydrogenase (GDH): one GDH utilizes NAD as coenzyme, the other uses NADP. The intracellular level of both GDHs is strongly regulated by the nitrogen source in the growth medium. NADP-dependent GDH was purified to homogeneity from crude extracts of The of the native enzyme was determined to be 200000 by size-exclusion high-performance liquid chromatography whereas after sodium dodecyl sulphate-polyacrylamide gel electrophoresis one major band of 49000 was found, suggesting that the enzyme is a tetramer. The enzyme was highly specific for the substrates 2-oxoglutarate and -glutamate, and required NADP, which could not be replaced by NAD, as a cofactor. The pH optimum was 9·2 for oxidative deamination of glutamate and 8·4 for reductive amination of 2-oxoglutarate. The Michaelis constants ( ) were 28·6 mM for -glutamate and 012 mM for NADP. values for reductive amination were 1·54 mM for 2-oxoglutarate, 007 mM for NADPH and 30·8 mM for NH . The enzyme activity was significantly reduced by adenine nucleotides, particularly ATP.


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