title: Guinea-pig kidney beta-N-acetylgalactosaminyltransferase towards Tamm-Horsfall glycoprotein. Requirement of sialic acid in the acceptor for transferase activity.
abstract: A beta-N-acetylgalactosaminyltransferase that preferentially transferred N-acetylgalactosamine to Sd(a-) Tamm-Horsfall glycoprotein was found in guinea-pig kidney microsomal preparations. This enzyme was kidney-specific and was able to transfer the sugar to other glycoproteins, such as fetuin and alpha 1-acidic glycoprotein. The presence of sialic acid in the acceptors was essential for the transferase activity when either glycoproteins or their Pronase glycopeptides were used as acceptors. Two glycopeptides (Tamm-Horsfall glycopeptides I and II) with a different carbohydrate composition were separated by DEAE-Sephacel chromatography from Pronase-digested Tamm-Horsfall glycoprotein. The amount of N-acetylgalactosamine transferred to glycopeptides by the enzyme correlated with their degree of sialylation. Enzymic digestion of N-[14C]acetylgalactosamine-labelled Tamm-Horsfall glycopeptide II showed that the transferred sugar was susceptible to beta-N-hexosaminidase. The amount of sugar cleaved by beta-hexosaminidase was strongly increased when the labelled Tamm-Horsfall glycopeptide II was pretreated with mild acid hydrolysis, a procedure that removed the sialic acid residues. Alkaline borohydride treatment of the labelled Tamm-Horsfall glycopeptide II did not release radioactivity, thus indicating that enzymic glycosylation took place at the N-asparagine-linked oligosaccharide units of Tamm-Horsfall glycoprotein.
mesh_terms: D000818:Animals; D001665:Binding Sites; D001789:Blood Group Antigens; D002241:Carbohydrates / Q000032:analysis; D002852:Chromatography, Ion Exchange; D005964:Glucosyltransferases / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism; D006168:Guinea Pigs; D007668:Kidney / Q000201:enzymology*; D008861:Microsomes / Q000201:enzymology; D009088:Mucoproteins / Q000378:metabolism*; D017351:N-Acetylglucosaminyltransferases / Q000378:metabolism*; D012794:Sialic Acids / Q000378:metabolism; D058949:Uromodulin
chemical_list: D001789:Blood Group Antigens; D002241:Carbohydrates; D006023:Glycoproteins; D009088:Mucoproteins; D012794:Sialic Acids; D058949:Uromodulin; D005964:Glucosyltransferases; D017351:N-Acetylglucosaminyltransferases; C024850:alpha-1,3-mannosyl-glycoprotein beta-1,2-N-acetylglucosaminyltransferase I