title: Human serum contains N-acetyllactosamine: beta 1-3 N-acetylglucosaminyltransferase activity.
abstract: Human serum was shown to contain N-acetyllactosamine: N-acetylglucosaminyltransferase activity. The reaction product was hydrolyzed by beta-N-acetylglucosaminidase and released [14C]N-acetylglucosamine, indicating that the N-acetylglucosaminyl residue was beta-linked to N-acetyllactosamine. Methylation and hydrolysis of the reaction product yielded 2,4,6-trimethyl[3H]galactose, indicating that the N-acetylglucosaminyl residue was introduced at position C-3 of the terminal galactose of N-acetyllactosamine. In our experiments, 2,3,4-trimethyl[3H]galactose was not detected. Substrate competition studies between N-acetyllactosamine and lactose showed that this enzyme also catalyzed the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to lactose. Since the Km value for N-acetyllactosamine, which was 7.0 mM, was approximately a fourth of that for lactose (29.8 mM), N-acetyllactosamine was more effective than lactose as an acceptor.
mesh_terms: D002250:Carbon Radioisotopes; D002413:Cations, Divalent; D005964:Glucosyltransferases / Q000097:blood*; D006801:Humans; D007700:Kinetics; D017351:N-Acetylglucosaminyltransferases; D014316:Tritium; D014531:Uridine Diphosphate Galactose; D014537:Uridine Diphosphate N-Acetylglucosamine
chemical_list: D002250:Carbon Radioisotopes; D002413:Cations, Divalent; D014316:Tritium; D014531:Uridine Diphosphate Galactose; D014537:Uridine Diphosphate N-Acetylglucosamine; D005964:Glucosyltransferases; D017351:N-Acetylglucosaminyltransferases; C042261:N-acetyllactosaminide beta-1,3-N-acetylglucosaminyltransferase