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Methyl glucoside hydrolysis catalyzed by beta-glucosidase
Emily B Golden1, Larry D Byers
1Department of Chemistry, Tulane University, New Orleans, LA 70118, USA.
Biochimica Et Biophysica Acta
|August 5, 2009
Summary
Sweet almond beta-glucosidase rapidly hydrolyzes glycosides. A stepwise mechanism, involving pre-equilibrium protonation and rate-limiting bond cleavage, explains the lack of a solvent kinetic isotope effect, highlighting enzyme stabilization of intermediates.
Area of Science:
- Biochemistry
- Enzymology
- Glycoside Hydrolase Research
Background:
- Sweet almond beta-glucosidase is a highly efficient family 1 glycohydrolase.
- It catalyzes glycoside hydrolysis at rates significantly exceeding spontaneous reactions.
Purpose of the Study:
- To elucidate the catalytic mechanism of sweet almond beta-glucosidase.
- To investigate the role of protonation and solvent effects in enzyme kinetics.
Main Methods:
- Kinetic analysis of enzyme activity in H2O and D2O.
- Determination of kinetic parameters (kcat/Km, Km) and inhibition constants (Ki).
- Assessment of solvent kinetic isotope effects.
Main Results:
- The enzyme exhibits bell-shaped pH dependence for kcat/Km, indicating catalytic residues.
- No significant solvent kinetic isotope effect was observed for kcat/Km or Km in D2O.
- Competitive inhibition patterns remained unchanged in D2O.
Conclusions:
- A stepwise mechanism involving pre-equilibrium protonation and rate-limiting glycosidic bond cleavage is proposed.
- Enzyme-induced stabilization of the protonated glucoside intermediate significantly contributes to rate enhancement.
- The catalytic mechanism is largely independent of solvent protonation state.
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