Ascorbate Peroxidase in Tea Leaves: Occurrence of Two Isozymes and the Differences in Their Enzymatic and Molecular Properties

Two isozymes of ascorbate (AsA) peroxidase were found in tealeaves, and one of them (AsA peroxidase II) was purified tohomogeneity, as judged by polyacrylamide gel electrophoresis.AsA peroxidase II is a monomer with a molecular weight of 34,000and contains protoheme, but it is not a glycoprotein. The enzymeshowed a Soret peak at 409 run and at 420 nm when oxidized andreduced, respectively, with an a-band at 556 nm. The oxidizedenzyme showed two small peaks at 478 nm and 530 nm. The peakat 478 nm disappeared when the enzyme was inactivated by depletionof AsA or by the addition of cyanide. Antibody raised againstAsA peroxidase II from tea did not cross-react with guaiacolperoxidase from spinach, and antibody against the guaiacol peroxidasedid not with AsA peroxidases from tea leaf. The amino acid compositionand amino acid sequence of the amino-terminal region of AsAperoxidase II were determined. Little homology in terms of aminoacid sequence was found between AsA peroxidase II and variousguaiacol peroxidases. The enzymatic and molecular propertiesof the two isozymes showed distinct differences with respectto molecular weight, sensitivity to AsA-depletion, specificityfor the electron donor, and other enzymatic properties. (Received April 13, 1989; Accepted July 25, 1989)