Role of Two Chloride-Binding Sites in Functioning of Testicular Angiotensin-Converting Enzyme

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N. A. Moiseeva^*, P. V. Binevski, I. I. Baskin, V. A. Palyulin, and O. A. Kost

Faculty of Chemistry, Lomonosov Moscow State University, 119992 Moscow, Russia; fax: (7-095) 939-5417; E-mail: znatali@enzyme.chem.msu.ru

^* To whom correspondence should be addressed.

Received December 28, 2004; Revision received February 1, 2005

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Modeling the structure of the C-domain of bovine angiotensin-converting enzyme revealed two putative chloride-binding sites. The kinetic parameters, K_m and k_cat, of hydrolysis of the substrate Cbz-Phe-His-Leu catalyzed by the testicular (C-domain) enzyme were determined over a wide range of chloride concentrations. Chloride anions were found to be enzyme activators at relatively low concentrations, but they inhibit enzymatic activity at high concentrations. A general scheme for the effect of chloride anions on activity of the C-domain of bovine angiotensin-converting enzyme accounting for binding the “activating” and “inhibiting” anions is suggested.

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KEY WORDS: angiotensin-converting enzyme, testicular enzyme, C-domain, chloride

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