Mitochondrial uptake and recycling of ascorbic acid

Mitochondria generate reactive oxygen species as by-products of oxidative m etabolism. Since ascorbic acid can scavenge such destructive species, we st udied the ability of mitochondria from rat liver and muscle to take up, rec ycle, and oxidize ascorbate. Freshly prepared mitochondria contain ascorbat e, as do mitoplasts that lack the outer mitochondrial membrane. Both mitoch ondria and mitoplasts rapidly take up oxidized ascorbate as dehydroascorbic acid and reduce it to ascorbate. Ascorbate concentrations in mitochondria and mitoplasts rise into the low millimolar range during dehydroascorbic ac id uptake, although uptake and reduction is opposed by ascorbate efflux. Mi tochondrial dehydroascorbic acid reduction depends mainly on GSH, but mitoc hondrial thioredoxin reductase may also contribute. Reactive oxygen species generated within mitochondria oxidize ascorbate more readily than they do GSH and cu-tocopherol. These results show that mitochondria can recycle asc orbate, which in turn might help to prevent deleterious effects of oxidant stress in the organelle. (C) 2001 Academic Press.