title: Probing the role of the hyper-reactive histidine residue of arginase.
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.
authors.affiliation: Department of Biochemistry, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Diana M
authors.initials: DM
authors.lastname: Colleluori
authors.forename: Robert S
authors.initials: RS
authors.lastname: Reczkowski
authors.forename: Frances A
authors.initials: FA
authors.lastname: Emig
authors.forename: Evis
authors.initials: E
authors.lastname: Cama
authors.forename: J David
authors.initials: JD
authors.lastname: Cox
authors.forename: Laura R
authors.initials: LR
authors.lastname: Scolnick
authors.forename: Kevin
authors.initials: K
authors.lastname: Compher
authors.forename: Kevin
authors.initials: K
authors.lastname: Jude
authors.forename: Shoufa
authors.initials: S
authors.lastname: Han
authors.forename: Ronald E
authors.initials: RE
authors.lastname: Viola
authors.forename: David W
authors.initials: DW
authors.lastname: Christianson
authors.forename: David E
authors.initials: DE
authors.lastname: Ash
mesh_terms: D000818:Animals; D001119:Arginase / Q000037:antagonists & inhibitors / Q000737:chemistry*; D001881:Borates / Q000737:chemistry; D018360:Crystallography, X-Ray; D004047:Diethyl Pyrocarbonate / Q000737:chemistry; D006639:Histidine / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009952:Ornithine / Q000737:chemistry; D011487:Protein Conformation; D051381:Rats
chemical_list: D001881:Borates; D006639:Histidine; D009952:Ornithine; D001119:Arginase; D004047:Diethyl Pyrocarbonate