This model describes a distinct clade of the Cys/Met metabolism pyridoxal phosphate-dependent enzyme superfamily. Members include examples of OAH/OAS sulfhydrylase, an enzyme with activity both as O-acetylhomoserine (OAH) sulfhydrylase (EC 2.5.1.49) and O-acetylserine (OAS) sulphydrylase (EC 2.5.1.47). An alternate name for OAH sulfhydrylase is homocysteine synthase. This model is designated subfamily because it may or may not have both activities. [Amino acid biosynthesis, Aspartate family, Amino acid biosynthesis, Serine family]