Mechanistic study of β-xylosidase from Trichoderma koningii G-39

Yaw-Kuen Li*, Hsin Jan Yao, I. Hong Pan

*Corresponding author for this work

Research output: Contribution to journalArticle

12 Scopus citations

Abstract

The catalytic mechanism of the β-xylosidase purified from the culture filtrate of Trichoderma koningii G-39 was investigated. By NMR spectroscopy, the stereochemistry of the enzyme catalyzing the hydrolysis of 2,4- dinitrophenyl and p-nitrophenyl-β-D-xylosides was found unequivocally to involve retention of the anomeric configuration. Based on the k(cat) values of a series of arylxylosides with leaving group pK(a)s in the range of 4-10, an extended Bronsted plot was constructed with a slope (β(lg)) near zero. Enzymatic hydrolysis of aryl-β-D-xylosides in acetate buffer (pH 4.0) containing 3 or 5% methanol showed a constant product ratio (methylxyloside/xylose), indicating the presence of a common intermediate, probably the xylosyl-enzyme intermediate. In the presence of DTT, the k(cat) values of p-cyanophenyl-β-D-xylopyranoside and p-nitrophenyl-β-D- xylopyranoside increased greatly. A two-step mechanism involving the formation and breakdown of the xylosyl-enzyme intermediate was therefore proposed. The rate-limiting step is the breakdown of the intermediate. The secondary deuterium kinetic isotope effect (k(H)/k(D)) measured for 2,4- dinitrophenyl-β-D-xyloside was 1.02±0.01, suggesting that the transition state for breakdown of the xylosyl-enzyme intermediate is S(N)2-like.

Original languageEnglish
Pages (from-to)315-320
Number of pages6
JournalJournal of Biochemistry
Volume127
Issue number2
DOIs
StatePublished - 1 Jan 2000

Keywords

  • Bronsted plot
  • Mechanism
  • Secondary deuterium isotope effect
  • β-xylosidase

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