The pyridoxal phosphate-dependent oxidative decarboxylation of methionine by peroxidase. I. Characteristics and properties of the reaction.

The most completely characterized peroxidase is horseradish peroxidase. It has been known for some time that this enzyme can act as an aerobic oxidase under certain conditions. Among the oxidative reactions catalyzed by this enzyme are the oxidation of dihydroxyfumaric acid (1, 2)) phenylacetaldehyde (3), phenylpyruvic acid (4)) dicarboxylic acids (5)) indoleacetic acid (6,7) reduced diphosphopyridine nucleotide, reduced triphosphopyridine nucleotide, ferrocytochrome c, and glutathione (8). In the presence of dihydroxyfumaric acid the enzyme also can carry out some hydroxylation reactions (9). All the foregoing reactions have shown a requirement for or stimulation by Mn++, and in many cases the presence of catalytic amounts of various phenols has great influence on the rate. In studies of sulfur amino acids as potential precursors of the volatile sulfur compounds implicated as the distinctive flavors and odors of some vegetables, the decarboxylation of methionine by an enzyme system from cabbage leaf particulate fractions was reported recently (10, 11). An absolute requirement for Mn++ and pyridoxal phosphate was demonstrated. The participation of a peroxide was indicated by catalase inhibition of the reaction. This paper presents experiments showing that highly purified horseradish peroxidase will also carry out this reaction and oxidatively decarboxylate methionine and several other amino acids. The presence of Mn++ and pyridoxal phosphate is obligatory. Some of the characteristics of this reaction are described.