On the oligosaccharide moiety of angiotensin-converting enzyme

Two glycopeptide fractions in a pronase digest of rabbit pulmonary angiotensin-converting enzyme were resolved by gel filtration. GP-I, the minor component (∼1 mole/mol enzyme) contained mannose, galactose, glucose N -acetylglucosamine, N -acetylgalactosamine and sialic acid in an approximate molar ratio of 1:5:3:4:1:2 and molar equivalents of aspartic acid, threonine and serine. GP-II, the major oligosaccharide unit (∼ 12 moles/mol enzyme, ∼ 90% of total carbohydrate), contained fucose, mannose, galactose, N -acetylglucosamine, sialic acid and aspartic acid in a molar ratio of 1:4:4:4:1:1. Although accounting for about one-quarter of the weight of the enzyme, GP-II did not compete with the intact glycoprotein for binding to goat antienzyme antibodies. Some structural features of GP-II were deduced by periodate oxidation and digestion with various glycosidases.