[Back to Number 9 ToC] [Back to Journal Contents] [Back to Biokhimiya Home page]

Kinetics of Inhibition of Green Crab (Scylla serrata) Alkaline Phosphatase by Vanadate

Q.-X. Chen1, W.-Z. Zheng1, J.-Y. Lin1, Z.-T. Cai1, and H.-M. Zhou1,2*

1Department of Biology, Xiamen University, Xiamen 361005, People's Republic of China

2Department of Biological Science and Biotechnology, Tsinghua University, Beijing 100084, People's Republic of China; fax: +8610 62785505; E-mail: zhm-dbs@mail.tsinghua.edu.cn

* To whom correspondence should be addressed.

Received February 14, 2000
Green crab (Scylla serrata) alkaline phosphatase is a metalloenzyme that catalyzes the nonspecific hydrolysis of phosphate monoesters. The kinetics of inhibition of the enzyme by vanadate has been studied. The time course of the hydrolysis of p-nitrophenyl phosphate catalyzed by the enzyme in the presence of different Na3VO4 concentrations showed that, at each Na3VO4 concentration, the rate decreased with increasing time until a straight line was approached, the slopes of the straight lines being the same for all concentrations. The results suggest that the inhibition of the enzyme by Na3VO4 is a slow, reversible reaction with fractional residual activity. The microscopic rate constants were determined for the reaction of the inhibitor with the enzyme. As compared with Na2HPO4 (Ki = 0.95 mM), Na2HAsO4 (Ki = 1.10 mM), and Na2WO4 (Ki = 1.55 mM), the results suggest that Na3VO4 (Ki = 0.135 mM) is a considerably more potent inhibitor than other inhibitors.
KEY WORDS: alkaline phosphatase, vanadate, inhibition, inactivation