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

Abstract

Two isozymes of ascorbate (AsA) peroxidase were found in tea leaves, and one of them (AsA peroxidase II) was purified to homogeneity, as judged by polyacrylamide gel electrophoresis. AsA peroxidase II is a monomer with a molecular weight of 34,000 and contains protoheme, but it is not a glycoprotein. The enzyme showed a Soret peak at 409 run and at 420 nm when oxidized and reduced, respectively, with an a-band at 556 nm. The oxidized enzyme showed two small peaks at 478 nm and 530 nm. The peak at 478 nm disappeared when the enzyme was inactivated by depletion of AsA or by the addition of cyanide. Antibody raised against AsA peroxidase II from tea did not cross-react with guaiacol peroxidase from spinach, and antibody against the guaiacol peroxidase did not with AsA peroxidases from tea leaf. The amino acid composition and amino acid sequence of the amino-terminal region of AsA peroxidase II were determined. Little homology in terms of amino acid sequence was found between AsA peroxidase II and various guaiacol peroxidases. The enzymatic and molecular properties of the two isozymes showed distinct differences with respect to molecular weight, sensitivity to AsA-depletion, specificity for the electron donor, and other enzymatic properties.