Colleluori DM, Reczkowski RS, Emig FA, Cama E, Cox JD, Scolnick LR, Compher K, Jude K, Han S, Viola RE, Christianson DW, Ash DE. Probing the role of the hyper-reactive histidine residue of arginase.
Arch Biochem Biophys 2005;
444:15-26. [PMID:
16266687 DOI:
10.1016/j.abb.2005.09.009]
[Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2005] [Revised: 09/14/2005] [Accepted: 09/14/2005] [Indexed: 11/15/2022]
Abstract
Rat liver arginase (arginase I) is potently inactivated by diethyl pyrocarbonate, with a second-order rate constant of 113M(-1)s(-1) for the inactivation process at pH 7.0, 25 degrees C. Partial protection from inactivation is provided by the product of the reaction, l-ornithine, while nearly complete protection is afforded by the inhibitor pair, l-ornithine and borate. The role of H141 has been probed by mutagenesis, chemical modulation, and X-ray diffraction. The hyper-reactivity of H141 towards diethyl pyrocarbonate can be explained by its proximity to E277. A proton shuttling role for H141 is supported by its conformational mobility observed among the known arginase structures. H141 is proposed to serve as an acid/base catalyst, deprotonating the metal-bridging water molecule to generate the metal-bridging hydroxide nucleophile, and by protonating the amino group of the product to facilitate its departure.
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