Glycoproteins and Blood Group Activity

Abstract

Abstract Three distinct serologically phenotypic mucins have been described in the hog submaxillary glands; A+, H+, and A-H- (In). Alkaline borohydride reductive cleavage of A+ and A- pig submaxillary mucin (A+-PSM and A--PSM) has enabled Carlson to propose structures for the oligosaccharides of these mucins. The structures presented readily explained the A+ and H+ cross-reactivity of the mucins, but left the structures of the In mucins unexplained. The relationship of H+ and In mucins and our previously published serological observations prompted us to determine the structures of the oligosaccharides isolated from inactive mucins secreted by hog submaxillary glands. In the present study, six oligosaccharides were isolated representing all of the potential combinations of imcomplete chains. The salient feature of this study is the demonstration of the attachment of sialic acid to galactose as well as to N-acetylgalactosaminitol. The structures of the three isolated acidic oligosaccharides are: a tetrasaccharide (I), α-l-fucopyranosyl-(1 → 2)-[N-glycolyl neuraminyl-(2 → 6)]-d-galactopyranosyl-(1 → 3)-2-acetamido-2-deoxy-d-galactitol; a trisaccharide (II), N-glycolyl neuraminyl-(2 → 6)-d-ga-lactopyranosyl-(1 → 3)-2-acetamido-2-deoxy-d-galactitol; and a disaccharide (III), N-glycolylneuraminyl-(2 → 6)-2-acetamido-2-deoxy-d-galactitol. Neutral oligosaccharides (IV, V, and VI) are the corresponding desialized materials. The structural features revealed are consonant with the observed serological phenomena and indicate the involvement of two sialyltransferases in the biosynthesis of the mucin. A possible biosynthetic pathway with the relative activity of the different glycosyltransferases is presented and discussed.