ABSTRACT
Uridine 5'-diphosphate glucose 4-epimerase (EC 5.1.3.2) from Ehrlich ascites carcinoma cells was purified to apparent homogeneity using conventional procedures and NAD-hexane-agarose affinity chromatography. The protein had a molecular weight of 96,000. The ascites enzyme had an absolute requirement for exogenously added NAD (10 μM) for stability. This appears to be a unique feature of ascites epimerase since epimerase from other mammalian sources did not exhibit such a dependence. Exogenously added NAD was also needed for catalysis with an apparent Km value of 2·5 μM. NADH was a very potent competitive inhibitor (K i = 0·11 μM with respect to NAD) of the enzyme activity at pH values close to intracellular pH. The dependence of the enzyme on NAD for stability and its inhibition by NADH may have some potential significance in tumor metabolism.