Characterization of N-acetyl-beta-d-galactosaminyl-transferase from guinea-pig kidney involved in the biosynthesis of Sda antigen associated with Tamm-Horsfall glycoprotein

This study reports the catalytic activity of N-acetyl-beta-D- galactosaminyltransferase from guinea-pig kidney towards such non- glycoprotein acceptors as small oligosaccharides and glycolipids, having a carbohydrate structure similar to that of the Sda antigen associated with human Tamm-Horsfall glycoprotein. 3'-O-Sialyllactose, but not 6'-O-sialyllactose or lactose, was an effective acceptor of the glycosyltransferase. On the basis of enzymic and chemical treatment of the tetrasaccharide obtained by the transfer of [14C]GalNAc to 3'-O- sialyllactose, we propose that the glycosyltransferase attaches beta-D- GalNAc to O-4 of the galactose residue that is substituted at O-3 by sialic acid. The GM3 ganglioside, in which the identical carbohydrate moiety of 3'-O-sialyllactose is bound to a ceramide residue, did not serve as an acceptor of the kidney-N-acetyl-beta-D- galactosaminyltransferase and did not behave as a competitive inhibitor of the Tamm-Horsfall glycoprotein in the transferase assay. These results indicate that the hydrophobic moiety in the ganglioside hinders the action of N-acetylgalactosaminyltransferase. Study of the transferase activity towards a heterogeneous glycopeptide species prepared from a Sd(a-) Tamm-Horsfall glycoprotein indicated that guinea- pig kidney enzyme preferentially transferred [14C]GalNAc to the oligosaccharides having a tetraantennary branching-structure