The effects of carbon source on glutamate dehydrogenase activities in Aspergillus nidulans.

The NADP-specific glutamate dehydrogenase (NADP-GDH) activity of Aspergillus nidulans was rapidly lost from cultures starved for a carbon source. This loss of NADP-GDH was blocked by protein synthesis inhibitors. Glutamate repressed NADP-GDH but did not cause rapid loss of activity. Since NADP-GDH is involved in the participation of ammonium in the regulation of nitrogen metabolism, the loss of NADP-GDH activity accompanying carbon starvation may be important in the interaction between carbon and nitrogen metabolism. Increased NAD specific glutamate dehydrogenase activity (NAD-GDH) was observed when mycelium was transferred to medium lacking glucose. The increase in NAD-GDH activity was greatest when glutamate was present. Protein synthesis inhibitors did not prevent this increase in activity. Two mutants, amdT102 and amdT19, which are altered in regulation of nitrogen metabolism, are similar to the wild-type strain with regard to regulation of NADP-GDH and NAD-GDH. Mutants in a gene, amdT, in Aspergillus nidulans pleiotropically affect the utilization of many nitrogen sources (Hynes, 1 9 7 3 ~). The utilization of L-glutamate is affected in arndT mutants. One mutant, amdT19, is unable to utilize glutamate as a sole nitrogen source in the presence of glucose, but grows normally on glutamate as the sole source of carbon and nitrogen. Another mutant, amdT102, grows slightly more strongly than wild-type strains on glutamate as the sole nitrogen source in the presence of glucose and is normal on glutamate as the sole carbon and nitrogen source. This has led to a study of the effects of the carbon source on glutamate metabolism. This paper describes the effects of the carbon source on glutamate dehydrogenase activities in the wild type as well as amdT mutants. Studies on glutamate uptake will be reported elsewhere (Hynes, 1973 b). Strains, iiiedin and genetic techniques. These have been described in previous papers Growth of nzjreliurn. Mycelium was grown as described previously (Hynes, 1972). In some experiments 20 to 30 ml of mycelium was sampled at various times and harvested by the normal method. Preparation qf cell-free extracts. Crude cell-free extracts were made in I 0-1 M-triS (hydroxy methyl) amino methane (tris)-hydrochloride buffer (pH 8.5) by the method of Hynes