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De Novo Synthesis of Peroxidase Isozymes in Sweet Potato Slices ^1,2

^a Laboratory of Biochemistry, Faculty of Agriculture, Nagoya University, Nagoya, Japan

The peroxidase content of sweet potato slices (Ipomoea batatas Lam.) increased nearly 100-fold following 84 hours incubation in an air atmosphere containing ethylene, 1 microliter per liter. The object of experiments reported here is to determine if this increase in peroxidase activity results from synthesis de novo of the enzyme or from activation of a preexisting inactive form of the enzyme.

The enzymatic activity of each peroxidase isozyme increased during the incubation period, and each peroxidase isozyme appeared to incorporate ¹⁴C-leucine. Polyacrylamide gel electrophoresis of the neutral peroxidase fraction showed that all peroxidase activity and essentially all radioactivity migrated as a single superimposable band. The other peroxidase fractions were less pure. Treatment of fresh slices, or slices collected midway in the time course with the inhibitor of protein synthesis, blasticidin S, (1 microgram per milliliter for one minute) caused an abrupt cessation of peroxidase formation and simultaneously an abrupt cessation of incorporation of ¹⁴C-leucine into peroxidase isozymes. These observations indicate that the rapid increase in peroxidase activity in sweet potato slices results from synthesis de novo of the enzyme.

⁴ Present address: Institute for Biochemical Regulation, Faculty of Agriculture, Nagoya University, Nagoya, Japan.

¹ This research was supported in part by the National Science Foundation and the Japan Society for the Promotion of Science through an award of a Visiting Scientist Grant under the auspices of the United States-Japan Cooperative Science Program.

² This paper constitutes Part 89 of the Phytopathological Chemistry of Sweet Potato with Black Rot and Injury.