Structure and location of the O-glycosidic carbohydrate units of human chorionic gonadotropin.

The carbohydrate structure of the O-glycosidicallylinked oligosaccharide chains in P-subunit of human chorionic gonadotropin (hCG$) and their precise number and locations in the polypeptide chains have been determined. A homogeneous preparation of the O-glycosidic oligosaccharide was obtained from NaOH/ NaBH,-treated human chorionic gonadotropin by chromatography on Dowex 50 and Sephadex G-25 and contained N-acetylneuraminic acid (NeuNAc), galactose, and N-acetylgalactosamine (GalNAc) in a ratio of 2: 1: 1. The structural determination of the carbohydrate was carried out by periodate oxidation, methylation using gas-liquid chromatography-mass spectrometry for the identification of methylated sugars and by treatment with specific glycosidases. The 0-glycosidic chains were found to have the following structure: