The 4-epimerization and decarboxylation of uridine diphosphate D-glucuronic acid by extracts from Phaseolus aureus seedlings.

It has been previously demonstrated (1) that particulate preparations from Phase&s uureus (mung bean) seedlings are capable of catalyzing the formation of uridine diphosphate-ngalacturonic acid1 and a mixture of UDP-n-xylose and UDP-Larabinose from UDP-n-glucuronic acid. The results indicated that the preparations contained UDP-uranic acid 4-epimerase and UDP-uranic acid decarboxylase activities. However, the individual reactions involved were not investigated. The work reported in this paper shows that three enzyme systems are operative in the conversions: a UDP-n-galacturonic acid-4-epimerase, a UDP-n-glucuronic acid decarboxylase, and a UDP-L-arabinose-4-epimerase. The enzyme systems catalyzing these reactions have been partially separated and the equilibrium constants have been determined for the two epimerization reactions.