Periodate oxidation studies of human pituitary follicle-stimulating hormone

Studies on pituitary follitropin. X. Biochemical, receptor binding and immunological properties of deglycosylated ovine hormone

Treatment of ovine pituitary follitropin with anhydrous hydrogen fluoride at 0 degrees C for 60 min resulted in the removal of approximately 80% of the sugars without affecting the polypeptide moiety. Fucose, sialic acid and N-acetylgalactosamine were eliminated completely while the loss of hexoses and N-acetylglucosamine amounted to 86% and 56% respectively. The treatment had no effect on the quaternary structure of the hormone. Consistent with the loss of carbohydrate, the elution volume of the hormone on Sephadex G100 was increased and the deglycosylated hormone lost its ability to interact with the lectin concanavalin-A immobilized on Sepharose. Deglycosylation rendered the hormone less acidic as reflected by altered electrophoretic mobility in polyacrylamide gels at pH 8.9 and 4.5. The UV absorption spectrum of the hormone was not affected by deglycosylation but tryptophan fluorescence was slightly decreased. The receptor-binding activity of the hormone as estimated by a specific radioreceptor assay using adult bovine testicular membranes and labeled 125I-FSH was increased by 250% following deglycosylation. In a conformation specific radioimmunoassay, the deglycosylated hormone showed 150% activity as compared to the native hormone. Thus, the full integrity of the carbohydrate moiety in ovine follitropin is not required for effective receptor binding and immunological activity.

The structures of the carbohydrate moieties of the alpha subunit of human chorionic gonadotrophin

The alpha subunit of human chorionic gonadotrophin was reduced with dithiothreitol followed by carboxymethylation with iodoacetic acid. The modified glycoprotein was hydrolysed with trypsin to give various peptides, the identities of which were established, and glycopeptides. The glycopeptides were separated by gel filtration and ion-exchange chromatography; they were subjected to component analysis and were found to represent the two carbohydrate moieties in the parent glycoprotein. Sequential removal with glycoside hydrolases of monosaccharide units from the glycopeptides demonstrated (1) that galactose, mannose, glucosamine (2-amino-2-deoxyglucose) and neuraminic acid (5-amino-3,5-dideoxy-glycero-galacto-2-nonulosonic acid) residues possess the D configurations, (2) that the glucosamine units are N-acetylated and (3) the order of the monosaccharide units in the chain, the neuraminic acid units being furthest from the peptide backbone of the subunit and substituting the D-galactose units. Methylation analysis of the glycopeptides by adaptation of the Hakomori technique demonstrated that: (4) D-galactose, D-mannose and N-acetylglucosamine (2-acetamido-2-deoxy-D-glucose) units exist in the pyranose forms; (5) the D-galactopyranose units are linked in the 1 and 6 positions; (6) the D-mannopyranose units exist in several forms, one in a terminal non-reducing position, one as 1,2-linked residues and some as 1,6-linked branch points; (7) the N-acetylglucosamine units are 1,6-linked. On the basis of the results of methylation and enzymic analysis, structures are proposed for the carbohydrate moieties and the assignments are compared with other data previously obtained by periodate-oxidation studies [Kennedy et al. (1974) Carbohydr. Res. 36, 369-377].

Structural investigation of the carbohydrate element of human pituitary follicle-stimulating hormone by methylation analysis

A preparation of human follicle-stimulating hormone has been subjected to methylation analysis by using the methyl sulphinyl carbanion-dimethyl sulphoxide-methyl iodide method. The hydrolysis products of the methylated glycoprotein were reduced, acetylated, analysed by gas-phase chromatography and mass spectrometry and identified by comparison with standards. Methylation analysis demonstrated that (1) the d-galactose, mannose, fucose and 2-amino-2-deoxyglucose units exist in the pyranose forms, (2) the 2-amino-2-deoxyglucose units are N-acetylated, (3) the fucopyranose units occupy terminal non-reducing positions, (4) the d-galactopyranose units are linked in the 1- and 2-positions, (5) the mannopyranose units exist in three forms, some as terminal non-reducing residues, some as 1,6-linked residues and some as 1,3,4-linked branch points, and (6) the 2-acetamido deoxyglucopyranose units are 1,6-linked. These structural assignments are compared with other data previously obtained for the carbohydrate moieties of follicle-stimulating hormone.