A SPECIFIC ASCORBATE FREE-RADICAL REDUCTASE ISOZYME PARTICIPATES IN THE REGENERATION OF ASCORBATE FOR SCAVENGING TOXIC OXYGEN SPECIES IN POTATO-TUBER MITOCHONDRIA

Ascorbate free radical (AFR) reductase from isolated potato tuber (Sol anum toberosum L.) mitochondria was studied. The enzyme was purified t o homogeneity and its physico-chemical and kinetic properties were com pared to those of the cytosolic enzyme. The molecular mass of the mito chondrial enzyme was about 54 kD, whereas that of the cytosolic enzyme was about 42 kD. The K-m values of mitochondrial AFR reductase for NA DH, NADPH, acid AFR were higher than those of the cytosolic enzyme. Mo reover, the mitochondrial enzyme proved to be less sensitive to inhibi tion by sulfhydryl reagents. It was concluded that the ascorbate invol ved in the scavenging of toxic oxygen species in potato tuber mitochon dria is regenerated via the ascorbate-glutathione pathway, in which a specific AFR reductase isozyme participates.