Enzymatic Studies on Ascorbic Add Catabolism in Animals

The enzymatic delactonization of de hydro-L-ascorbic acid in animal tissue was described with the assay condition without loss of resulting diketogulonic acid at pH of the physiological range. The enzyme was purified, and properties including proportionality of the reaction to time and enzyme concentration, cofactor requirement, stoichiometry, inhibitors, and the absence of the reverse reaction were described. The reaction product was confirmed as 2,3-diketo-L-gulonic acid. The enzyme was possibly identical to lactonase I (aldonolactonase) in almost all the properties tested and they were not separated from each other though esterases and lactonase II (uronolactonase) were removed in the course of enzyme purification. The role of this enzyme in this irreversible process of ascorbic acid catabolism and physiological findings caused by the lack of its activity in primates were discussed.