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. 1992 May 1;283 ( Pt 3)(Pt 3):679-82.

Chemical mechanism of beta-glucosidase from Trichoderma reesei QM 9414. pH-dependence of kinetic parameters

I de la Mata  1 , P Estrada, R Macarrón, J M Dominguez, M P Castillón, C Acebal
Affiliations

Chemical mechanism of beta-glucosidase from Trichoderma reesei QM 9414. pH-dependence of kinetic parameters

I de la Mata et al. Biochem J. .

Abstract

The variation of kinetic parameters of beta-glucosidase from Trichoderma reesei QM 9414 with pH was used to gain information about the chemical mechanism of the reaction catalysed by this enzyme. The pH-dependence of Vmax. and Vmax./Km for p-nitrophenyl beta-D-glucopyranoside showed that a group with a pK value of 4.3 must be unprotonated and a group with a pK value of 5.9 must be protonated for activity. Temperature and solvent-perturbation studies indicated that these groups are a histidine residue and a carboxy group respectively. Profiles of pKi for maltose as competitive inhibitor showed that binding is prevented when a group on the enzyme with a pK value of 4.5 becomes protonated.

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