Lack of binding of serum glycoprotein hormone α subunit to Concanavalin A–Sepharose reflects increased branching of the oligosaccharide chains

in Journal of Endocrinology
Authors:
A. J. Chapman
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J. T. Gallagher
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C. G. Beardwell
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S. M. Shalet
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ABSTRACT

The lectin-binding properties of serum α subunit were studied by lectin affinity chromatography. Normal individuals and most patients with pituitary tumours produced α subunit which bound specifically to Concanavalin A–Sepharose (Con A). Some patients with pituitary tumours produced both Con A-reactive α subunit and α subunit which did not bind to Con A. Concanavalin A–Sepharose-binding α subunit from all sources bound strongly to Ricinus communis agglutinin–Sepharose after treatment with neuraminidase. Serum α 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 α 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 α 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 α subunit from normal controls is a Con A-reactive, biantennate complex oligosaccharide and (b) that the structural alteration which results in serum α subunit which does not bind to Con A in some patients with pituitary tumours is not an absence of carbohydrate, rather the α subunit contains highly branched, either complex or hybrid oligosaccharides.

J. Endocr. (1984) 103, 111–116

 

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