General Control of Arginine Biosynthetic Enzymes in Neurospora crassa

Abstract

The response of 6 amino acid synthetic enzymes, including 4 concerned with arginine synthesis, 1 with histidine synthesis and 1 with lysine synthesis, to conditions of histidine and arginine limitation and to exogenously provided amino acids is described in N. crassa. The activities of all these enzymes increased in response to lowered levels of histidine or arginine but showed little or no repression in wild-type cultures supplemented with casein hydrolysate. The activity of glucose-6-phosphate dehydrogenase remained unaffected by any of these conditions. The general system implicated in the cross-pathway response to histidine is also entirely responsible for the derepression occurring under conditions of arginine limitation. Further investigations into the control of 1 enzyme, ornithine carbamoyltransferase, are reported. The enzyme is stable and suggest that its derepression in response to histidine limitation entails new protein synthesis and involves control at a stage prior to translation.