Formation of L-lyxonic and L-xylonic acids from L-ascorbic acid in rat kidney.

The enzymatic decarboxylation of n-ascorbic acid by rat kidney homogenates has been reported in an earlier study (1). It was shown that factors present in both the soluble and the particulate fractions were required for maximal activity. Evidence was presented suggesting that dehydro-L-ascorbic acid and 2,3-diketo-n-gulonic acid were intermediates in the decarboxylation of the vitamin. The reaction products were not identified at that time, although the formation of n-xylose and n-xylulose was excluded. More recently, evidence for the identity of the products as n-xylonic and n-lyxdnic acids has been reported briefly (2). An alternate ascorbic acid-metabolizing system present in the soluble fraction of guinea pig liver has been shown by Chan et al. (3). In this case, L-xylose was identified as a product of the decarboxylation of dehydroascorbic acid. The present communication is concerned with a description of the partially purified enzyme system from rat kidney and with further documentation on the identification of n-lyxonic and n-xylonic acids as the major products arising from the decarboxylation of diketogulonic acid. The reactions studied are illustrated in Fig. 1.