Studies on the oligosaccharide chains of human alpha 1-protease inhibitor. I. Isolation of glycopeptides.

Cyanogen bromide fragments of alpha 1-protease inhibitor (PI) were chromatographed on Sephadex G-75. Three fragments (CNBr-I, -II, and -III) contained carbohydrates with nearly the same composition, i.e. Man3, Gal2-3, (GlcNAc)4-5, and (NeuAc)2-3. These three fragments were digested with pronase, and the glycopeptides were purified by column chromatography on Sephadex G-50, Bio-Gel P-4, and DEAE-cellulose. The carbohydrate and amino acid compositions of the glycopeptides obtained by these treatments demonstrated that oligosaccharide side chains are attached to three asparaginyl residues which are located in separate regions of the polypeptide chain, and that the carbohydrate chains are made of two different carbohydrate compositions. The A-chain consists of Man3, Gal2, (GlcNAc)4, and (NeuAc)2, and the B-chain consists of Man3, Gal3, (GlcNAc)5, and (NeuAc)3. CNBr-III contained only A-type oligosaccharide while CNBr-II contained both A-type and B-type oligosaccharides in a ratio of about 2:1. CNBr-I, derived from the NH2 terminus of PI, contained mainly A-type, but also some B-type oligosaccharide.