PLANT PHYSIOLOGY , Vol 109, Issue 3 847-851, Copyright © 1995 by American Society of Plant Biologists
|
BIOCHEMISTRY AND ENZYMOLOGY |
A Specific Ascorbate Free Radical Reductase Isozyme Participates in the Regeneration of Ascorbate for Scavenging Toxic Oxygen Species in Potato Tuber Mitochondria
S. De Leonardis, G. De Lorenzo, G. Borraccino and S. Dipierro
Plant Physiology Laboratory, Institute of Botany, University of Bari, 70126 Bari, Italy
Ascorbate free radical (AFR) reductase from isolated potato tuber (Solanum
tuberosum L.) mitochondria was studied. The enzyme was purified to
homogeneity and its physico-chemical and kinetic properties were compared
to those of the cytosolic enzyme. The molecular mass of the mitochondrial
enzyme was about 54 kD, whereas that of the cytosolic enzyme was about 42
kD. The Km values of mitochondrial AFR reductase for NADH, NADPH, and AFR
were higher than those of the cytosolic enzyme. Moreover, the mitochondrial
enzyme proved to be less sensitive to inhibition by sulfhydryl reagents. It
was concluded that the ascorbate involved in the scavenging of toxic oxygen
species in potato tuber mitochondria is regenerated via the
ascorbate-glutathione pathway, in which a specific AFR reductase isozyme
participates.