Studies on Monooxygenases

Crystalline l-lysine monooxygenase from Pseudomonas fluorescens catalyzes the incorporation of 1 atom of molecular oxygen into the substrate, l-lysine, concomitant with a decarboxylation to form δ-amino-n-valeramide. In addition to l-lysine, the l isomers of several basic amino acids such as 2,7-diaminoheptanoate, arginine, δ-hydroxylysine, and S-aminoethylcysteine serve as the substrate for the monooxygenation catalyzed by the enzyme. When l-ornithine was incubated with the enzyme, however, it was converted to α-keto-δ-amino-n-valerate with the consumption of oxygen and with the formation of ammonia and hydrogen peroxide in stoichiometric amounts. These findings suggest that l-lysine monooxygenase can catalyze an oxidative deamination of l-ornithine similar to that catalyzed by l-amino acid oxidase. 2,8-Diaminooctanoate appeared to be degraded in the same way as l-ornithine as evidenced by a 50% reduction in the rate of oxygen uptake upon the addition of catalase. Evidence indicating that both activities, monooxygenation and oxidation of amino acids, are attributable to a single enzyme includes the constant ratio of the two activities during the course of the enzyme purification and the parallel inactivation by —SH inhibitors or by sodium dodecyl sulfate. A competitive type inhibition of lysine monooxygenation by ornithine suggests that both amino acids bind to the enzyme at the same site.