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. Zhou^1,2*

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

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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 (K_i = 0.95 mM), Na₂HAsO₄ (K_i = 1.10 mM), and Na₂WO₄ (K_i = 1.55 mM), the results suggest that Na₃VO₄ (K_i = 0.135 mM) is a considerably more potent inhibitor than other inhibitors.

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KEY WORDS: alkaline phosphatase, vanadate, inhibition, inactivation

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