Two immunologically different isozymes of ascorbate peroxidase from spinach leaves.

Two isozymes of ascorbate peroxidase (AP) from spinach leaves were separated by hydrophobic chromatography and designated AP-I and AP-II. They had similar molecular weights of about 31,000, as determined by gel-filtration, and showed high specificity for ascorbate. One of the two isozymes (AP-II) was purified to homogeneity by SDS-PAGE. Immunoblotting confirmed that antiserum against AP-II reacted with AP-II but not with AP-I. This antiserum inhibited the activity of AP-II, but not that of AP-I. The amino acid composition and partial amino acid sequence of AP-II were determined.