Characterization of N-acetyl-β- d-galactosaminyl-transferase from guinea-pig kidney involved in the biosynthesis of Sd a antigen associated with tamm-horsfall glycoprotein

Abstract

This study reports the catalytic activity of N-acetyl-β- d-galactosaminyl-transferase from guinea-pig kidney towards such non-glycoprotein acceptors as small oligosaccharides and glycolipids, having a carbohydrate structure similar to that of the Sd a 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 β-d-GalNAc to O-4 of the galactose residue that is substituted at O-3 by sialic acid. The G M3 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-β- 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.