title: Mucin synthesis. III. UDP-GlcNAc:Gal beta 1-3(GlcNAc beta 1-6)GalNAc-R (GlcNAc to Gal) beta 3-N-acetylglucosaminyltransferase, an enzyme in porcine gastric mucosa involved in the elongation of mucin-type oligosaccharides.
abstract: Pig gastric mucosa microsomes have been shown to catalyze the following reaction: UDP-GlcNAc + Gal beta 1-3(GlcNAc beta 1-6)-GalNAc-alpha-R----GlcNAc beta 1-3Gal beta 1-3 (GlcNAc beta 1-6)GalNAc-alpha-R + UDP, where R is o-nitrophenyl or benzyl. The enzyme catalyzing this reaction has been named UDP-GlcNAc:Gal beta 1-3(GlcNAc beta 1-6)GalNAc-R (GlcNAc-R (GlcNAc to Gal) beta 3-N-acetylglucosaminyltransferase. The beta 3-GlcNAc-transferase does not act on Gal beta 1-3GalNAc-alpha-o-nitrophenyl. The beta 3-GlcNAc-transferase requires Mn2+ and Triton X-100 for optimal activity. The Vmax for the microsomal enzyme is 8.7 nmol/mg protein per hour and the Km values are 1.6, 0.9, and 1.2 mM for UDP-GlcNAc and the alpha-o-nitrophenyl and alpha-benzyl derivatives of Gal beta 1-3(GlcNAc beta 1-6)GalNAc, respectively. Pig gastric mucosa microsomes catalyze the transfer of GlcNAc to lactose to form GlcNAc beta 1-3Gal beta 1-4Glc, but fail to transfer GlcNAc to lactosyl ceramide, Gal beta 1-4GlcNAc, or Gal beta 1-4GlcNAc-beta-benzyl.
mesh_terms: D000818:Animals; D002250:Carbon Radioisotopes; D002645:Chickens; D004285:Dogs; D005260:Female; D005753:Gastric Mucosa / Q000201:enzymology*; D005964:Glucosyltransferases / Q000302:isolation & purification / Q000378:metabolism*; D008861:Microsomes / Q000201:enzymology; D009077:Mucins / Q000096:biosynthesis*; D017351:N-Acetylglucosaminyltransferases; D009928:Organ Specificity; D010057:Oviducts / Q000201:enzymology; D013045:Species Specificity; D013363:Submandibular Gland / Q000201:enzymology; D013379:Substrate Specificity; D013552:Swine
chemical_list: D002250:Carbon Radioisotopes; D009077:Mucins; D005964:Glucosyltransferases; D017351:N-Acetylglucosaminyltransferases; C027732:UDP-N-acetylglucosamine-mucin acetylglucosaminyltransferase