title: One-proton catalysis by the alpha-L-arabinofuranosidase III of Monilinia fructigena.
abstract: 1. Michaelis-Menten parameters for the hydrolysis of p-nitrophenyl alpha-L-arabinofuranoside were measured as a function of pL (pH or pD) in both 1H2O and 2H2O. 2. The variation of both Vmax. and Vmax./Km with pL is sigmoid, the pK governing Vmax. shifting from 6.34 +/- 0.05 in 1H2O to 6.84 +/- 0.07 in 2H2O, and that governing Vmax./Km from 5.89 +/- 0.03 in 1H2O to 6.38 +/- 0.05 in 2H2O. 3. In the plateau regions there is a small inverse solvent isotope effect on Vmax./Km (0.92), and one of 1.45 on Vmax. 4. The variation of Vmax. with isotopic composition is strictly linear, indicating that the isotope effect arises from the transfer of a single proton.
authors.affiliation: Department of Organic Chemistry, University of Bristol, U.K.
authors.forename: T
authors.initials: T
authors.lastname: Selwood
authors.forename: M L
authors.initials: ML
authors.lastname: Sinnott
mesh_terms: D001089:Arabinose / Q000031:analogs & derivatives / Q000378:metabolism; D001203:Ascomycota / Q000201:enzymology*; D006026:Glycoside Hydrolases / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D011522:Protons
chemical_list: D011522:Protons; C017567:4-nitrophenyl-alpha-L-arabinofuranoside; D001089:Arabinose; D006026:Glycoside Hydrolases; C019713:alpha-N-arabinofuranosidase