InterPro domain: IPR014033

L-Arginine is converted to nitric oxide and citrulline by the enzyme nitric oxide synthase and by the enzyme arginase as a part of the hepatic urea cycle [ 1 ]. Arginase is a manganese metalloenzyme containing a metal-activated hydroxide ion, a critical nucleophile in metalloenzymes that catalyze hydrolysis or hydration reactions. A hydrogen bond formed by the metal-bound hydroxide holds the enzyme in the proper orientation for catalysis however non-metal substrate-binding sites are also implicated in the enzyme mechanism. Regeneration of metal-bound hydroxide ion from a metal-bound water molecule requires proton transfer to bulk solvent mediated by a histidine proton shuttle residue.

1. Phylogeny of related functions: the case of polyamine biosynthetic enzymes. Microbiology (Reading, Engl.) 146 ( Pt 8), 1815-28