Carbohydrate structures of bovine kidney gamma-glutamyltranspeptidase

The carbohydrate moieties of gamma-glutamyltranspeptidase (gamma-GTP) purified from bovine kidney were chemically released as oligosaccharides. The oligosaccharide mixture was fractionated into a neutral fraction and three groups of acidic fractions containing one, two, and three sialic acid residues. Both the neutral fractions and the neutral oligosaccharide mixture obtained from the pooled sample of all acidic fractions by sialidase treatment were separated into seven components by Bio-Gel P-4 column chromatography. Structural studies of these components by sequential exoglycosidase digestion in combination with methylation analysis indicated that the gamma-GTP contains at least twelve neutral sugar chains which are either the high mannose type, or the bi- and triantennary complex type, and thirteen acidic sugar chains of the bi-, tri-, and tetraantennary complex type. The characteristics feature of the sugar chains of the gamma-GTP is that most of the complex type sugar chains contain an N-acetylglucosamine residue at the C-4 position of the beta-mannosyl residue of their trimannosyl core, and their outer chain moieties are enriched in non-reducing terminal beta-N-acetylglucosamine residues.