Mucins prosthetic groups

Fig. 4. The major prosthetic group of ovine submaxillary mucin, i.e., W-acetyl-neuraminyl-( 2->6)-A/-acetyl-D-galactosaminyl-serine.

Present knowledge on the biosynthesis of the prosthetic groups of OSM and porcine submaxillary mucin (PSM) is summarized in Fig. 12. Five glycosyltransferases are required for the synthesis of the most complex oligosaccharide side chain, the pentasaccharide present in PSM with human blood group A specificity (Carlson, 196, Section II). Four of these five enzymes are required for the synthesis of the side chain of blood group A-negative PSM two transferases are required for incorporation of the disaccharide side chain of OSM. 

Two families of antibodies have been found to be generated after immunization of rabbits with ovine submaxillary mucin. In the case of subcutaneous immunization, the immunodominant determinants are the prosthetic N-acetyl-neuraminosyl-2-acetamido-2-deoxy-D-galactopyranosyl and the 2-acetamido-2-deoxy-D-galactopyranosyl groups, but intravenous immunization of the glycoprotein coupled to red blood cells elicits, in addition, antibodies with specificities for the apoprotein. 

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