An Essential Tryptophan Residue in Alkaline Phosphatase from Pearl Oyster (Pinctada fucata)

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Li-Ping Xie^1,2, Guang-Rui Xu¹, Wei-Zhong Cao¹, Jin Zhang¹, and Rong-Qing Zhang^1,2*

¹Institute of Marine Biotechnology, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, 100084, China; fax: +86 (010) 6277-2899; E-mail: rqzhang@mail.tsinghua.edu.cn

²Protein Science Laboratory of the Ministry of Education, Tsinghua University, Beijing, 100084, China

^* To whom correspondence should be addressed.

Received May 4, 2007; Revision received June 4, 2007

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Alkaline phosphatases are ubiquitous enzymes found in most species including the pearl oyster, Pinctada fucata, where it is presumably involved in nacreous biomineralization processes. In the present study, we have purified alkaline phosphatases from the pearl oyster and modified the tryptophan residues using N-bromosuccinimide (NBS). We show that the resulting inactivation of purified alkaline phosphatase by NBS is dependent on modification of only one of five tryptophan residues in the enzyme. Substrate protection experiments showed that the tryptophan residue was not located at the substrate-binding site but was involved in the catalytic activity.

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KEY WORDS: alkaline phosphatase, Pinctada fucata, chemical modification, kinetics

DOI: 10.1134/S0006297908010136

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