Isozymes of glutamate dehydrogenase from oat leaves : Properties and light effect on synthesis

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Ammonium-dependent induction of a GDH isozyme in oat leaves was proportional to light intensity and inhibited by DCMU. The stimulation of GDH synthesis in response to ammonia was partially repressed by benzimidazole. The inducible (no. 1) and noninducible (no. 2) GDH isozymes were separated and purified by approximately 54 and 24 fold respectively. The two isozymes were highly specific for NAD and the rate of NADH oxidation was 7 to 9 times higher than NAD reduction. Both isozymes showed similar Km values for substrates of the reductive amination reaction and pH optima for NADH oxidation. The pH optima for NAD reduction were 9 and 8.2 for isozymes 1 and 2 respectively. The two isozymes had a similar molecular weight, 2.2-2.4 × 10^5 but differed in their isoelectric point and temperature sensitivity. Results suggest that the GDH isozymes in oat leaves are two different entities but might possess a similar metabolic function.