Glycosyltransferases in human blood.I. Galactosyltransferase in human serum and erythrocyte membranes.
Human serum and hemoglobin-free erythrocyte membranes were found to contain a galactosyltransferase which catalyzes the transfer of galactose from UDP-galactose to specific large and small molecular weight acceptors. The requirements for enzyme activity were found to be similar for the enzymes from both sources. However, the membrane-bound enzyme depended on a detergent for maximal activity. Mn(++) was an absolute requirement for transfer and uridine nucleoside phosphates were inhibitors. The most effective acceptor for galactose was a glycoprotein containing N-acetylglucosamine residues in the terminal position of its oligosaccharide side chains, N-acetylglucosamine was also an acceptor. While the presence of alpha-lactalbumin in the incubation medium resulted in a significant decrease in the transfer of galactose to N-acetylglucosamine, glucose, which was not an acceptor for galactose in the absence of alpha-lactalbumin, became an excellent acceptor. The serum enzyme catalyzed the transfer of 54 nmoles of galactose per milliliter of serum per hour and its apparent K(m) for UDP-galactose was 7.5 x 10(-6)M. The membrane enzyme had a similar apparent K(m). Using a quantitative assay system the enzyme was found to be present in all individuals studied, regardless of their blood type, secretor status, or sex.
D000017:ABO Blood-Group System; D000418:Albumins / Q000494:pharmacology; D003902:Detergents / Q000494:pharmacology; D004912:Erythrocytes / Q000201:enzymology*; D005260:Female; D005690:Galactose; D005944:Glucosamine / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism; D006602:Hexosyltransferases / Q000097:blood*; D006801:Humans; D008297:Male; D008345:Manganese / Q000378:metabolism; D008566:Membranes / Q000201:enzymology; D008722:Methods; D009077:Mucins; D014500:Uracil Nucleotides / Q000494:pharmacology
D000017:ABO Blood-Group System; D000418:Albumins; D003902:Detergents; D006023:Glycoproteins; D009077:Mucins; D014500:Uracil Nucleotides; D008345:Manganese; D006602:Hexosyltransferases; D005947:Glucose; D005944:Glucosamine; D005690:Galactose