Studies on Monooxygenases

In order to elucidate the function of FAD, a cofactor of l-lysine monooxygenase, in the oxygenation of substrate, experiments were carried out with a substrate amount of enzyme. Under anaerobic conditions the enzyme-bound FAD was essentially fully reduced by an equimolar amount of substrate, l-lysine. The rate of FAD reduction was found to be dependent on the substrate concentration. When FAD was reduced with lysine and then the reaction mixture was deproteinized in the absence of oxygen, lysine was found to be converted to α-keto-e-aminocaproate (Δ1-piperidine 2-carboxylate), which was identified by paper electrophoresis, ion exchange column chromatography, and paper chromatography. In contrast to the aerobic reaction, essentially no carbon dioxide was produced. When the reduced FAD was reoxidized with air prior to deproteinization, the keto acid was also formed. The mechanism of formation of keto acid in these experiments was compared with the reaction mechanism of amino acid oxidase and discussed in relation to the oxygenation of lysine.