Regeneration of Ascorbic Acid by Rat Colon

Abstract

Abstract

Plants and animals alike use ascorbic acid in a variety of reactions that result in net generation of dehydro-l-ascorbic acid. The ability to reduce dehydro-l-ascorbic acid back to ascorbic acid would conserve “total ascorbate” and would help to maintain the toxic oxidized form of the molecule at a low level. This study evaluated the rate of dehydro-l-ascorbic acid reduction either by following the rate of NADPH consumption or by analysis of the amount of ¹⁴C-labeled dehydro-l-ascorbic acid converted to ascorbic acid. A large percentage of the NADPH consumed by a semipurified preparation of rat colonic mucosa in vitro was dependent on the presence of dehydro-l-ascorbic acid. The tissue factor active in regenerating ascorbic acid is intermediate in size between cytochrome c and blue dextran. The present results indicate that the mucosa reduced dehydro-l-ascorbic acid by a cytosolic enzyme that uses NADPH as a hydrogen donor. Subsequent to precipitation by ammonium sulfate, the 55–70% fraction contains most of the reductase activity while consisting of only 17% of the cellular soluble protein.