UDP-N-acetyl-D-galactosamine as a donor substrate for the glycosyltransferase encoded by the B gene at the human blood group ABO locus.
The properties of the enzyme in the serum of blood group B individuals that catalyses the transfer of small amounts of N-acetyl-D-galactosamine to H-active precursor structures were compared with those of the blood group B gene-associated alpha-(1----3)-D-galactosyltransferase and with the blood group A gene-associated alpha-(1----3)-N-acetyl-D-galactosaminyltransferases in the serum of blood group A1 and A2 individuals. The biosynthetic products formed by the enzyme in B serum were identical with the A-active structures synthesised by the A1 and A2 gene-associated alpha-(1----3)-N-acetyl-D-galactosaminyltransferases but the enzyme differed from the A1 and A2 transferases in its apparent Km for UDP-N-acetyl-D-galactosamine, its heat susceptibility, its failure to bind to Sepharose 4B, and its adsorption to H-active sites on group O red cell ghosts under conditions which bind the B transferase but fail to adsorb the A1 and A2 transferases. The correlation between the levels of alpha-(1----3)-D-galactosyltransferase and alpha-(1----3)-N-acetyl-D-galactosaminyltransferase activities in all the group B serum samples tested, the maintenance of the same ratio of activities after successive cycles of binding to group O red cell ghosts, the retention of the ability to convert blood group O to A-active cells after treatment of the serum with Sepharose 4B, and the failure to detect any comparable activity in group O serum samples tested under the same conditions indicated that the enzyme in group B serum that utilises UDP-N-acetyl-D-galactosamine to make blood group A-active structures is the B gene-associated alpha-(1----3)-D-galactosyltransferase.
D000017:ABO Blood-Group System / Q000235:genetics*; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002250:Carbon Radioisotopes; D005700:Galactosyltransferases / Q000235:genetics* / Q000378:metabolism; D005796:Genes; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D017350:N-Acetylgalactosaminyltransferases; D014536:Uridine Diphosphate N-Acetylgalactosamine / Q000378:metabolism*; D014539:Uridine Diphosphate Sugars / Q000378:metabolism*
D000017:ABO Blood-Group System; D002250:Carbon Radioisotopes; D014539:Uridine Diphosphate Sugars; D014536:Uridine Diphosphate N-Acetylgalactosamine; D005700:Galactosyltransferases; D017350:N-Acetylgalactosaminyltransferases; C003742:UDPgalactosamine-galactose acetylgalactosaminyltransferase; C023155:blood-group-substance alpha-D-galactosyltransferase