Affiliations: Department of Medicine, Vanderbilt University School
of Medicine, Nashville, TN, USA | Department of Molecular Physiology and Biophysics,
Vanderbilt University School of Medicine, Nashville, TN, USA
Note: [] Address for correspondence: Dr. James May, 7465 Medical Preston
Research Building, Vanderbilt University School of Medicine, Nashville, TN
37232-0475, USA. Tel.: +1 615 936 1653; Fax: +1 615 936 1667; E-mail:
james.may@vanderbilt.edu
Abstract: Mitochondria are the major source of potentially damaging reactive
oxygen species in most cells. Since ascorbic acid, or vitamin C, can protect
against cellular oxidant stress, we studied the ability of mitochondria
prepared from guinea pig skeletal muscle to recycle the vitamin from its
oxidized forms. Although ascorbate concentrations in freshly prepared
mitochondria were only about 0.2 mM, when provided with 6 mM succinate and 1 mM
dehydroascorbate (the two-electron-oxidized form of the vitamin), mitochondria
were able to generate and maintain concentrations as high as 4 mM, while
releasing most of the ascorbate into the incubation medium. Mitochondrial
reduction of dehydroascorbate was strongly inhibited by
1,3-bis(chloroethyl)-1-nitrosourea and by phenylarsine oxide. Despite existing
evidence that mitochondrial ascorbate protects the organelle from oxidant
damage, ascorbate failed to preserve mitochondrial
α-tocopherol during prolonged incubation in oxygenated
buffer. Nonetheless, the capacity for mitochondria to recycle ascorbate from
its oxidized forms, measured as ascorbate-dependent ferricyanide reduction, was
several-fold greater than total steady-state ascorbate concentrations. This,
and the finding that more than half of the ascorbate recycled from
dehydroascorbate escaped the mitochondrion, suggests that mitochondrial
recycling of ascorbate might be an important mechanism for regenerating
intracellular ascorbate.
