Lack of binding of serum glycoprotein hormone alpha subunit to concanavalin A-Sepharose reflects increased branching of the oligosaccharide chains.
The lectin-binding properties of serum alpha subunit were studied by lectin affinity chromatography. Normal individuals and most patients with pituitary tumours produced alpha subunit which bound specifically to Concanavalin A-Sepharose (Con A). Some patients with pituitary tumours produced both Con A-reactive alpha subunit and alpha subunit which did not bind to Con A. Concanavalin A-Sepharose-binding alpha subunit from all sources bound strongly to Ricinus communis agglutinin-Sepharose after treatment with neuraminidase. Serum alpha subunit from those patients with pituitary tumours, which did not bind to Con A, bound to wheat germ agglutinin-Sepharose, exhibiting both weakly binding and strongly binding forms. Serum alpha subunit from both patients and controls, which did bind to Con A, showed only weak affinity for wheat germ agglutinin-Sepharose. Neither the low affinity nor the high affinity of serum alpha subunit from any source for wheat germ agglutinin-Sepharose was affected by neuraminidase. These findings show that (a) the predominant pattern of glycosylation of serum alpha subunit from normal controls is a Con A-reactive, biantennate complex oligosaccharide and (b) that the structural alteration which results in serum alpha subunit which does not bind to Con A in some patients with pituitary tumours is not an absence of carbohydrate, rather the alpha subunit contains highly branched, either complex or hybrid oligosaccharides.
D000328:Adult; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003208:Concanavalin A / Q000378:metabolism*; D005260:Female; D015292:Glycoprotein Hormones, alpha Subunit; D006801:Humans; D037102:Lectins / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009844:Oligosaccharides / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism*; D010908:Pituitary Hormones, Anterior / Q000378:metabolism*; D010911:Pituitary Neoplasms / Q000032:analysis; D037121:Plant Lectins; D011485:Protein Binding; D012685:Sepharose / Q000378:metabolism; D014909:Wheat Germ Agglutinins
D015292:Glycoprotein Hormones, alpha Subunit; D037102:Lectins; D009844:Oligosaccharides; D010446:Peptide Fragments; D010908:Pituitary Hormones, Anterior; D037121:Plant Lectins; C017707:Ricinus communis agglutinin-1; D014909:Wheat Germ Agglutinins; D003208:Concanavalin A; D012685:Sepharose