Mucin biosynthesis. Properties of a bovine tracheal mucin beta-6-N-acetylglucosaminyltransferase.
We have characterized a bovine tracheal mucin beta-6-N-acetylglucosaminyltransferase that catalyses the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to the C-6 of the N-acetylgalactosamine residue of galactosyl-beta 1----3-N-acetylgalactosamine. Optimal enzyme activity was obtained between pH 7.5-8.5, at 5mM-MnCl2, and at 0.06-0.08% (v/v) Triton X-100 (or Nonidet P-40), or 0.5-5.0% (v/v) Tween 20. Ba2+, Mg2+ and Ca2+ could partially replace Mn2+, but Co2+, Fe2+, Cd2+ and Zn2+ could not. Sodium dodecyl sulphate, cetylpyridinium chloride, sodium deoxycholate, octyl beta-D-glucoside, digitonin and alkyl alcohols were less effective in enhancing enzyme activity, and dimethyl sulphoxide was ineffective. The apparent Michaelis constants were 1.25 mM for UDP-N-acetylglucosamine, 0.94-3.34 mM for freezing-point-depressing glycoprotein and 0.19 mM for periodate-treated blood-group-A porcine submaxillary mucin. Asialo ovine submaxillary mucin could not serve as the glycosyl acceptor. The structure of the 14C-labelled oligosaccharide obtained by alkaline-borohydride treatment of the product was identified as Gal beta 1----3(Glc-NAc beta 1----6)N-acetylgalactosaminitol by beta-hexosaminidase treatment, gas chromatography-mass spectrometry and 1H-n.m.r. (270 MHz) analysis. The enzyme is important in the regulation of mucin oligosaccharide biosynthesis.
D000438:Alcohols / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D002712:Chlorides / Q000494:pharmacology; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D003902:Detergents / Q000494:pharmacology; D005700:Galactosyltransferases / Q000378:metabolism*; D008968:Molecular Conformation; D009077:Mucins / Q000096:biosynthesis*; D017350:N-Acetylgalactosaminyltransferases; D014132:Trachea / Q000201:enzymology*; D014312:Trisaccharides / Q000302:isolation & purification; D000097763:Polypeptide N-acetylgalactosaminyltransferase
D000438:Alcohols; D002712:Chlorides; D003902:Detergents; D005700:Galactosyltransferases; D009077:Mucins; D017350:N-Acetylgalactosaminyltransferases; D014312:Trisaccharides; D000097763:Polypeptide N-acetylgalactosaminyltransferase