Studies on the Reduction of Dehydroascorbic Acid by Guinea Pig Tissues*

It has been suggested frequently that one of the functions of ascorbic acid (vitamin C) in the animal organism may be that of a respiratory catalyst (l-6). The factors responsible for the postulated reversible oxidation and reduction of ascorbic acid by animal tissues have been poorly defined, however. Aside from the qualitative observation (1) that ‘(hexuronic acid” slowly reduced cytochrome C, animal tissue constituents responsible for the oxidation of ascorbic acid, either directly or by catalysis, have not been identified. The reduction of dehydroascorbic acid by animal tissues, based on urinary excretion (4, 7) and tissue storage (8) of ascorbic acid after administration of dehydroascorbic acid, has been attributed to glutathione by Borsook et al. (4), although the possibility of enzymic reduction (9) has not been excluded. The observation of Szent-Gyorgyi (1) that reversibly oxidized hexuronic (ascorbic) acid could be reduced by fixed -SH and glutathione has been followed by quantitative experiments by Hopkins and Morgan (3) and by Borsook et al. (4). The last two papers cited review the available evidence that tissues tend to protect ascorbic acid from oxidation. Recently Masayama and Tatematsu (10) reported that very small amounts of tissue could exert this protection and Yamamoto (11) found that Z-adrenalin was similarly effective. Glutathione (12214) in small quantities, boiled tissues (15), and other substances forming copper complexes (16) can inhibit the aerobic oxidation of ascorbic acid by