title: The mechanism of action of beta-glucosidase from Botryodiplodia theobromae Pat.
abstract: The activity of the high-molecular-weight beta-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) obtained from culture filtrates of Botryodiplodia theobromae Pat. was affected by added NaCl in such a way that an initial phase of stimulation was followed by a phase of rapid non-linear decrease in velocity and finally by a phase of slow linear decrease in velocity as the concentration of NaCl was increased. In the presence of 0.014 M-sodium acetate/acetic acid buffer (pH 5.0) there was a slight increase in enzymic activity in the presence of low concentrations of dioxan (up to about 10% dioxan) and a rapid decrease in enzymic activity at higher dioxan concentrations, but both effects were mitigated in the presence of 0.1 M buffer. The order of efficiency of added glucosyl acceptors in beta-glucosidase-catalysed reactions was found to be fructose greater than sucrose greater than glycerol greater than methanol. The enzyme was inactivated by the active-site-directed compound conduritol-B-epoxide; but this inactivation was concentration-dependent, was prevented by 10 mM-glucose, and involved an acidic group with pKa 4.3. A rate equation has been derived on the assumption of a mechanism of action involving a solvent-separated and an intimate glucosyl cation-carboxylate ion-pair intermediate and an alpha-glucosyl enzyme intermediate [Umezurike, G. M. (1981) Biochem. J. 199, 203-209]. Calculations based on the application of the derived rate equation and the calculated kinetic parameters show that the rate equation explains the peculiar properties of beta-glucosidase in the presence of added glucosyl acceptors or of NaCl.
mesh_terms: D004146:Dioxanes / Q000494:pharmacology; D005959:Glucosidases / Q000378:metabolism*; D005990:Glycerol / Q000494:pharmacology; D007294:Inositol / Q000031:analogs & derivatives / Q000494:pharmacology; D007700:Kinetics; D003904:Mitosporic Fungi / Q000201:enzymology*; D012965:Sodium Chloride / Q000494:pharmacology; D001617:beta-Glucosidase / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D004146:Dioxanes; D012965:Sodium Chloride; D007294:Inositol; D005959:Glucosidases; D001617:beta-Glucosidase; C025223:1,4-dioxane; C011423:conduritol epoxide; D005990:Glycerol