Abstract
Degradation of L-ascorbic acid proceeds from dehydroascorbic acid, which is in turn hydrolyzed irreversibly by liver supernatant fraction to form 2,3-diketo-L-gulonic acid. This heat labile degradative factor was purified about 10-fold. The preparation had no esterase activity, but the activity was accompanied by lactonase I activity, The low activity of this dehydroascorbic acid hydrolysing enzyme in primates is correlated with the slow rate of ascorbic acid metabolism in these species. 2,3-Diketo-L-gulonic acid is further degraded nonenzymatically under aerobic condition to L-threonic acid, oxalic acid and carbon dioxide. Enzymatically, however, this compound is decarboxylated by 2,3-diketoaldonic acid decarboxylase forming isomeric products, L-lyxonic acid and L-xylonic acid. This enzyme was purified about 50-fold from rat liver supernatant. The products were identified as a form of benzimidazole crystals. Further metabolism of these three L-aldonic acids produced from ascorbic acid was also examined. The significance of ascorbic acid degradation was discussed.
