Roles of O-acetyl-L-homoserine sulfhydrylases in micro-organisms.

O-Acetyl-L-homoserine sulfhydrylase (EC 4.2.99.10) is essential for certain micro-organisms, functioning as a homocysteine synthase in the pathway of methionine synthesis. It participates in an alternative pathway of L-homocysteine synthesis for those microbes in which homocysteine is synthesized mainly via cystathionine. The protein can also catalyze the de novo synthesis of L-cysteine and O-alkyl-L-homoserine in some microorganisms. The enzyme possibly recycles the methylthio group of methionine.