Amine oxidation by d-arginine dehydrogenase in Pseudomonas aeruginosa

Abstract d -Arginine dehydrogenase from Pseudomonas aeruginosa ( Pa DADH) is a flavin-dependent oxidoreductase, which is part of a novel two-enzyme racemization system that functions to convert d -arginine to l -arginine. Pa DADH contains a noncovalently linked FAD that shows the highest activity with d -arginine. The enzyme exhibits broad substrate specificity towards d -amino acids, particularly with cationic and hydrophobic d -amino acids. Biochemical studies have established the structure and the mechanistic properties of the enzyme. The enzyme is a true dehydrogenase because it displays no reactivity towards molecular oxygen. As established through solvent and multiple kinetic isotope studies, Pa DADH catalyzes an asynchronous CH and NH bond cleavage via a hydride transfer mechanism. Steady-state kinetic studies with d -arginine and d -histidine are consistent with the enzyme following a ping-pong bi-bi mechanism. As shown by a combination of crystallography, kinetic and computational data, the shape and flexibility of loop L1 in the active site of Pa DADH are important for substrate capture and broad substrate specificity.