title: Direct homocysteine biosynthesis from O-succinylhomoserine in Escherichia coli: an alternate pathway that bypasses cystathionine.
abstract: Mutations were found which enable Escherichia coli K-12 to form homocysteine in the absence of cystathionase. The formation of homocysteine in the mutant strains required cystathionine gamma-synthetase, the metB gene product, but bypassed the normal intermediate cystathionine. It is concluded that cystathionine gamma-synthetase catalyzes the formation of homocysteine directly from O-succinylhomoserine and an as-yet-unidentified sulfur donor. The mutation apparently causes the formation of this sulfur donor and has been named metQ. The expression of the metQ gene is under catabolite repression.
mesh_terms: D019757:Carbon-Oxygen Lyases; D003540:Cystathionine / Q000378:metabolism; D003542:Cystathionine gamma-Lyase / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D006710:Homocysteine / Q000096:biosynthesis*; D006714:Homoserine / Q000031:analogs & derivatives* / Q000378:metabolism; D008190:Lyases / Q000378:metabolism*; D009154:Mutation
chemical_list: D006710:Homocysteine; C014196:O-succinylhomoserine; D003540:Cystathionine; D006714:Homoserine; C022696:O-succinylhomoserine (thiol)-lyase; D008190:Lyases; D019757:Carbon-Oxygen Lyases; D003542:Cystathionine gamma-Lyase