Catalyzes the conversion of O-acetyl-L-homoserine (OAH) into homocysteine in the methionine biosynthesis pathway (PubMed:9440513, PubMed:12832650). Can also use O-succinyl-homoserine (OSH), although at low efficiency (PubMed:12832650). hydrogen sulfide + O-acetyl-L-homoserine = acetate + L-homocysteine Feedback inhibited at very high concentrations of methionine or S-adenosylmethionine. Amino-acid biosynthesis; L-methionine biosynthesis via de novo pathway; L-homocysteine from O-acetyl-L-homoserine: step 1/1. Belongs to the trans-sulfuration enzymes family.