Abstract
Three pseudomonad monooxygenases, salicylate hydroxylase, imidazoleacetate hydroxylase and lysine oxygenase, were purified and identified to be flavoproteins. Their prosthetic flavin was flavin adenine dinucleotide. Since neither iron nor copper was detected in a significant quantity, the flavin seemed to be a sole prosthetic group of these enzymes. These and other flavooxygenases comprise a major new group of flavoproteins. Lysine oxygenase catalyzed an oxygenative decarboxylation of lysine producing an acid amide. Under anaerobic conditions, however, the enzyme showed a dehydrogenation of lysine and produced a corresponding α-keto acid. Upon the modification of the enzyme protein by sulfhydryl blocking reagents, the enzyme now catalyzed an oxidative deamination of lysine producing an α-keto acid and hydrogen peroxide. Furthermore, certain analogues such as ornithine and γ-methyllysine underwent an oxidative deamination. α-Monoamino acids were also oxidized, but only when alkylamines were present. Thus, an oxidase activity was demonstrated by the modification of either the enzyme or the substrate. The significance of this oxidase activity is discussed in terms of the oxygen activation by the flavin.
