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

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

*Corresponding author for this work

研究成果: Article同行評審

12 引文 斯高帕斯(Scopus)

摘要

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.

原文English
頁(從 - 到)315-320
頁數6
期刊Journal of Biochemistry
127
發行號2
DOIs
出版狀態Published - 1 一月 2000

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