| Abstract: | Lysine monooxygenase catalyzes the oxygenation of lysine and arginine, and produces delta-amino-n-valeramide and gamma-guanidinobutyramide, respectively, concomitant with decarboxylation. In a preliminary communication, treatment of the native enzyme with p-chloromercuribenzoate was shown to inactivate the oxygenase and to induce an oxidase activity. The modified enzyme catalyzed predominantly the oxidative deamination of lysine and arginine resulting in the formation of the corresponding alpha-keto acid, ammonia, and hydrogen peroxide (YAMAUCHI, T., YAMAMOTO, S., and HAYAISHI, O.(1973) J. Biol. Chem. 2j8, 3750-3752). Paper electrophoresis, cellulose thin layer chromatography, and chemical degradation of the reaction products from lysine and arginine, provided further evidence for their identity with alpha-keto-epsilon-aminocaproate and alpha-keto-delta-guanidinovalerate, respectively. Further studies were carried out to establish the involvement of sulfhydryl groups in this conversion of the enzyme activities. Various sulfhydryl reagents including certain mercurials, alkylating, and oxidizing reagents, showed essentially identical effects on the enzyme. Dithiothreitol treatment reversed the conversion produced by various mercurials; the oxidase activity disappeared and the oxygenase activity was recovered. When p-chloromercuribenzoate was added to the enzyme and the increase in the absorbance at 250 nm was followed, 3.6 of the 6.5 half-cystine residues present per enzyme-bound FAD were readily titrated within 3 to 4 min. The inactivation of the oxygenase and the induction of the oxidase activity were almost maximal with 4 to 5 mol of p-chloromercuribenzoate/mol of enzyme, and these effects occurred within 3 to 4 min. These results together with other properties of the modified enzyme provided evidence for a possible involvement of these reactive sulfhydryl groups during the conversion of the oxygenase to an oxidase. |
