title: Control of glycoprotein synthesis. Kinetic mechanism, substrate specificity, and inhibition characteristics of UDP-N-acetylglucosamine:alpha-D-mannoside beta 1-2 N-acetylglucosaminyltransferase II from rat liver.
abstract: Purified rat liver UDP-GlcNAc:alpha-D-mannoside beta 1-2 N-acetylglucosaminyltransferase II (Bendiak, B., and Schachter, H. (1987) J. Biol. Chem. 262, 5775-5783) has been characterized kinetically, and its substrate specificity and inhibition characteristics have been determined. Kinetic data indicate an ordered, or largely ordered sequential mechanism, with UDP-GlcNAc binding prior to the acceptor. The minimal acceptor structure required for full activity is: (Formula: see text) The acceptor molecule must have a terminal Man alpha 1-6 residue, and a terminal GlcNAc beta 1-2Man alpha 1-3 branch to display any activity, but does not require the reducing GlcNAc residue, as the enzyme was about 50% as active after reduction of this residue to N-acetylglucosaminitol. Additional residues (Gal beta 1-4 on the GlcNAc beta 1-2Man alpha 1-3 arm, or a bisecting GlcNAc beta 1-4 on the beta-Man residue) abolish catalytic activity. These results suggest a rigid order in the biosynthesis of all N-linked complex oligosaccharides (bisected and nonbisected bi-, tri-, and tetraantennary), since the enzyme must act to completion prior to the action of either UDP-Gal:GlcNAc beta 1-4 galactosyltransferase or N-acetylglucosaminyltransferase III to make such structures. Inhibition studies with nucleotides, sugars, nucleotide-sugars, and their respective analogues revealed that analogues of UDP and UTP, in which the hydrogen at the 5 position of the uracil was substituted with -CH3, bromine, or mercury (as the mercaptide) were good reversible inhibitors of the enzyme, whereas substitution at other sites lessened the inhibitory potency, usually to a large degree.
mesh_terms: D000818:Animals; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D005964:Glucosyltransferases / Q000378:metabolism*; D006020:Glycopeptides / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D017351:N-Acetylglucosaminyltransferases; D009844:Oligosaccharides / Q000378:metabolism; D051381:Rats; D013379:Substrate Specificity
chemical_list: D006020:Glycopeptides; D006023:Glycoproteins; D009844:Oligosaccharides; D005964:Glucosyltransferases; D017351:N-Acetylglucosaminyltransferases; C063313:alpha-1,6-mannosyl-glycoprotein beta-1,2-N-acetylglucosaminyltransferase