Effect of Environmental Conditions on the NADP-Specific Glutamic Acid Dehydrogenase in Neurospora crassa

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Abstract
The chemical form and quantity of nitrogen sup-plied during the growth of wild-type Neurospora crassa mycelia had a significant effect on total protein synthesis and NADP-specific glutamate-dehydrogenase (NADP-GD) specific activity. Both NADP-GD-specific activity and protein yields were high when NH4+ was the sole nitrogen source. At NH4+ concentrations up to the optimal for protein synthesis, NADP-GD production and protein synthesis were proportional; at higher concentrations NADP-GD specific activity decreased disproportionately. Glutamate alone, more markedly glutamate + NH4+, or a mixture of amino acid (e.g. sodium caseinate), similarly depressed NADP-GD-specif ic activity. These data support the contention that excess nitrogen in some form acts as a specific NADP-GD repressor. Evidence is presented from experiments with nitrogen-starved mycelia that low concentrations of NH4+ per se may act to de-repress NADP-GD production. Under conditions of early nitrogen starvation, followed by a short growth period after NH4+ supplementation, more than 1% of the soluble protein in a heat-treated extract was found to be NADP-GD.