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.
Highlights
Lysine monooxygenasecatalyzes the oxygenation of lysine and arginine, and produces &amino-n-valeramide and yguanidinobutyramide, respectively, concomitant with decarboxylation
Evidence to be presented in this paper suggests that the appearance of this oxidase activity coincides with the modification of sulfhydryl groups of the enzyme
With the native enzyme 79% of the arginine consumed was oxygenated to y-guanidinobutyramide, while the remaining 21% was subjected to electrophoresis with a-keto-6-guanidinovalerate
Summary
Lysine monooxygenasecatalyzes the oxygenation of lysine and arginine, and produces &amino-n-valeramide and yguanidinobutyramide, respectively, concomitant with decarboxylation. The inactivation of the oxygenaseand 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 evidencefor a possibleinvolvement of these reactive sulfhydryl groups during the conversion of the oxygenaseto an oxidase. As has been described in a preliminary communication [5], a careful treatment of the enzyme with p-MB decreased the oxygenase activity, but concomitantly an oxidase activity was induced as observed with the oxygenase-type substrates such as lysine and arginine (Equation 2).
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