Argininosuccinate synthetase of Neurospora crassa

The argininosuccinate synthetase ( l-citrulline: l-aspartate ligase (AMP), E.C.6.3.4.5) of Neurospora crassa has been studied in crude extracts and in partially purified form. The conditions necessary for enzyme activity resemble closely those previously described for the corresponding enzyme from other sources. Both l-α-amino- n-butyric acid and l-arginine are competitive inhibitors with respect to citrulline. It is suggested that the in vivo depression of the arginine pool size during growth of the mold in the presence of aminobutyrate is in part the result of inhibition of argininonuccinate synthetase by this amino acid.