Studies on the Fermentative Production and Metabolism of Uridine Coenzymes

Part II. NAD-Dependent UDPGal-4-Epimerase in Torulopsis candida and its Inactivation by 5'-UMP and Galactose

Abstract

A partially purified preparation of UDPGal-4-epimerase from lactosegrown Torulopsis candida was found to require exogenous NAD for the full activity, while little activity being observed without NAD. The Km for NAD was 1.4×10^-4 M, showing a relatively low affinity as compared with the enzymes from mammalian sources. The enzyme activits was remarkably inhibited by incubation with 5'-UMP provided that galactose was also present. The concentration of 5'-UMP present seemed more critical than that of galactose on the inhibition; it occurred in the presence of low concentration of 5'-UMP provided that galaetose was present enough. The catalytic activity was almost recovered by a short dialysis of the enzyme preparations preincubated with 5'-UMP and galactose. A strong inactivation of the enzyme activity was also found by the combination of 5'-UMP and glucose.