Catalyzes the conversion of O-acetyl-L-homoserine (OAH) into homocysteine in the methionine biosynthesis pathway. Has weak activity with O-acetyl-L-serine, O-phospho-L-serine, L-serine, O-succinyl-L-homoserine and L-homoserine. Shows low CTT beta-lyase activity and very low CTT gamma-synthase activity. hydrogen sulfide + O-acetyl-L-homoserine = acetate + L-homocysteine Inhibited by the carbonyl reagents hydroxylamine and phenylhydrazine. Also inhibited by methionine and propargylglycine. Optimum pH is 7.8. Shows high pH stability over a wide range of pH (pH 4-12). Optimum temperature is 70 degrees Celsius. Very stable at high temperature. 90% of the activity is retained after treatment at 90 degrees Celsius for 60 min. Amino-acid biosynthesis; L-methionine biosynthesis via de novo pathway; L-homocysteine from O-acetyl-L-homoserine: step 1/1. Homotetramer. Belongs to the trans-sulfuration enzymes family.