Chemical mechanism of beta-glucosidase from Trichoderma reesei QM 9414. pH-dependence of kinetic parameters.
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.
de la Mata
I
I
Departamento de Bioquímica y Biología Molecular I, Facultad de Química, Universidad Complutense, Madrid, Spain.
Estrada
P
P
Macarrón
R
R
Dominguez
J M
JM
Castillón
M P
MP
Acebal
C
C
D001667:Binding, Competitive; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D005960:Glucosides / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008320:Maltose / Q000494:pharmacology; D011522:Protons; D012997:Solvents; D013696:Temperature; D013816:Thermodynamics; D014242:Trichoderma / Q000201:enzymology*; D001617:beta-Glucosidase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*
D005960:Glucosides; D011522:Protons; D012997:Solvents; C025193:4-nitrophenyl beta-D-glucoside; D008320:Maltose; D001617:beta-Glucosidase