Sialic acids. 13. A uridine diphosphate D-galactose: mucin galactosyltransferase from porcine submaxillary gland.

Abstract A particulate galactosyltransferase isolated from pig submaxillary glands catalyzed the transfer of galactose from uridine diphosphate galactose to both high and low molecular weight derivatives of N-acetylgalactosamine (2-acetamido-2-deoxy-d-galactopyranosides). The most effective acceptor for this enzyme was sialidase-treated ovine submaxillary mucin. The product of this reaction was galactosyl → N-acetylgalactosaminyl → protein, which is an intermediate in the biosynthesis of the more complex oligosaccharides of porcine submaxillary mucin. However, the enzyme does not transfer galactose to sialic acid-containing oligosaccharides. Thus, the relative activities of the UDP-galactose:mucin galactosyltransferase reported here, and the previously described CMP-sialic acid:mucin sialyltransferase may act as the controlling mechanism for determining the final structures of the oligosaccharide units in the submaxillary mucins. The enzyme preparation also contained two previously described galactosyltransferases which utilized N-acetylglucosamine (or serum-type glycoproteins containing N-acetylglucosamine end groups) and Tay-Sachs ganglioside, respectively, as galactose acceptors. The enzyme described here was distinguished from the previously reported enzymes by acceptor specificity and competition studies.