Cysteine biosynthesis in Aspergillus nidulans.

The existence of two postulated pathways of anabolic cysteine biosynthesis in Aspergillus midulans was investigated. No activities of the postulated pathway involving S-sulfocysteine as intermediate have been detected. Investigations on cyteine and methionine requiring mutants revealed independent regulation of O-acetylserine sulfhydrylase by endogeneous cysteine and methionine pools. The reaction catalysed by O-acetylserine sulfhydrylase is postulated as the only anabolic pathway of cysteine biosynthesis in A. nidulans.