Purification and characterization of an ascorbate peroxidase from potato tuber mitochondria

Ascorbate peroxidase (APX) has been purified from potato tuber (Solanum tuberosum L.) mitochondria. The potato enzyme appeared to be localized inside mitochondria. The mitochondrial APX was purified to homogeneity and its physico-chemical and kinetic properties were compared with those of the cytosolic enzyme. The molecular mass of mAPX was 31 kDa, as estimated by SDS-PAGE, and was similar to that of the cytosolic enzyme, but its relative mobility in non-denaturing PAGE was different from the cytosolic APX. The Km values of mAPX for AsA and H2O2 were 76.1 ± 23.1 and 80.3 ± 24.9 μM, respectively, and were higher than those of the cytosolic enzyme. Mitochondrial APX was sensitive to inhibition by sulfhydryl reagents, such as mersalyl and p-hydroxymercuribenzoate (p-HMB). A role for the mitochondrial ascorbate-ascorbate peroxidase system in the scavenging of toxic oxygen species inside potato tuber mitochondria is proposed.