Enzymatic Studies on Ascorbic Acid Catabolism in Animals

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Abstract
Potassium 2, 3-diketo-L-gulonate was synthesized and its metabolism in animal tissues was studied to clarify the catabolism of ascorbic acid. Metabolic products of diketogulonate in vitro were confirmed as L-lyxonic acid and L-xylonic acid in the presence of decarboxylase of diketogulonate in neutral condition, and as L-threOnic acid and oxalic acid in aerobic alkaline condition. All three aldonic acids were isolated and crystallized in the form of benzimidazole derivatives. Formation of the same metabolic products was also detected in vivo. The enzyme, 2, 3-diketoaldonate decarboxylase, which catalysed the decarboxylation of diketogulonic acid and other diketoaldonic acids, was purified about 50 fold from rat liver supernatant. Properties of the decarboxylase, including substrate affinity constant and stoichiometry were described. The enzyme is distributed in liver and kidney supernatant fraction of animals including primates.