The Carbohydrate Moiety of Human Chorionic Gonadotropin: Lack of Competition with HCG for Testicular Receptors and Anti-HCG-Serum

Abstract

A glycopeptide fraction has been prepared from human chorionic gonadotropin (HCG) by digesting the reduced, S-carboxymethylated hormone with pronase and fractionating the digest by gel exclusion chromatography. The glycopeptide fraction was estimated to contain (w/w) 29% sialic acid, 31% hexose, 23% hexosamine, and 17% amino acids and/or peptides; thus, the glycopeptide mixture is 83% carbohydrate compared to intact HCG which is about 30% carbohydrate. There was no cross-reactivity of the glycopeptide fraction with an antiserum directed against HCG. Also, when corrected for minimal non-specific effects, the fraction failed to displace ¹²⁵I-HCG from a rat testicular preparation even when tested at a 10,000-fold (w/w) excess. Thus, any model involving carbohydrate effects in gonadotropin action must include the protein moiety as a necessary component.

Key words

Human Chorionic Gonadotropin - Glycopeptides - Radio-Immunoassay - Radio-Receptor Assay