Structure of the carbohydrate moieties of alpha subunits of human follitropin, lutropin, and thyrotropin.

Human follitropin, lutropin, thyrotropin, and their (Y and /3 subunits were prepared from the same batch of pituitary glands.The total carbohydrate content of human follitropin, lutropin, and thyrotropin was approximately 27.2%, 21.4%, and 21.1% by weight, respectively.N-Acetylgalactosamine was consistently present in all the hormones.In all hormones and their subunits, mannose and N-acetylglucosamine were present in a ratio of 1:l.The sialic acid and fucose contents were variable.The carbohydrate contents of human follitropin LY subunit and follitropin p subunit were similar, whereas the carbohydrate contents of human lutropin (x subunit and human thyrotropin a subunit were Z-fold greater than in their respective /3 subunits.Human follitropin, lutropin, and thyrotropin were subjected to pronase and thermolysin digestion and gel filtration on Sephadex G-50.The glycopeptide fractions were purified by high voltage paper electrophoresis.Two glycopeptides from follitropin-cu involving asparagine 52 and 78 and one each from lutropin-cw and thyrotropin-cu involving asparagine 52 were isolated.The variations in the number of sialic acid and fucose residues at terminal positions of the glycopeptides indicated microheterogeneity.The carbohydrate composition of these glycopeptides was found to be Fu+,, Gal,, Man4, GalNAc,, GlcNAc,, and NeuAco.The structure of the carbohydrate and peptide moieties of these glycopeptides was derived by sequential hydrolysis with specific glycosidases, by hydrolysis with endoglycosidases, by periodate oxidation, by alkaline degradation, and by Edman degradation.The peripheral portion of the carbohydrate moiety consists of three chains with the monosaccharide sequence of sialic acid L+ galactose L N-acetylglucosamine p. mannose.