title: Effect of added nucleophiles and pH on alpha-D-mannosidase-catalyzed reactions.
abstract: The effect of (1) added nucleophiles, (2) the concentration of water, and (3) pH on the alpha-D-mannosidase-catalyzed hydrolysis of substituted phenyl alpha-D-mannopyranosides has been investigated.. A two-step mechanism, with formation of a mannosyl-enzyme complex, is proposed. With the phenyl alpha-D-mannopyranosides, the formation of this intermediate complex is the rate-limiting step. The activity of the enzyme is controlled by two dissociable groups having pK approximately 3 and pK approximately 6, respectively. It is proposed that one of the groups functions as a proton-donor, whereas the other group stabilizes the mannosyl-enzyme complex by ion-pair formation or covalent binding.
mesh_terms: D000433:1-Propanol / Q000494:pharmacology; D000438:Alcohols / Q000494:pharmacology*; D004146:Dioxanes / Q000494:pharmacology; D004186:Disaccharidases / Q000378:metabolism*; D004355:Drug Stability; D000431:Ethanol / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008361:Mannosidases / Q000378:metabolism*; D008433:Mathematics; D000432:Methanol / Q000494:pharmacology; D012639:Seeds / Q000201:enzymology; D015032:Zinc / Q000494:pharmacology
chemical_list: D000438:Alcohols; D004146:Dioxanes; D000431:Ethanol; D000433:1-Propanol; D004186:Disaccharidases; D008361:Mannosidases; D015032:Zinc; D000432:Methanol