SUMMARY: The chemical form and quantity of nitrogen supplied during the growth of wild-type 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 NH+ was the sole nitrogen source. At NH+ 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 + NH+, or a mixture of amino acids (e.g. sodium caseinate), similarly depressed NADP-GD specific 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 NH+ may act to de-repress NADP-GD production. Under conditions of early nitrogen starvation, followed by a short growth period after NH+ supplementation, more than 1 % of the soluble protein in a heat-treated extract was found to be NADP-GD.


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