Uridinediphosphate glucose pyrophospho-rylase was purified 280 folds above the crude extract of E. coli K 12. With the use of the purified enzyme preparations, some of its properties were studied.K_m values for uridinediphosphate glucose, pyrophosphate, glucose-l-phosphate and uridinetriphosphate were calculated to be 1.3×l0^-4M; l.3×10^-4M, 4.8×10^-5M and 2.9×10^-5M, respectively. It had a broad pH optimum between 7.5. and 9.0. The equilibrium constant
K=[Glucose-l-phosphate] [Uridinetriphosphate]/[UDPglucose] [Pyrophosphate] was found to be 5.0. This result indicates that the reaction is favorable for the. degradation of uridinediphosphate glucose. The enzyme requires magnesium ion for its activity and is specific for uridinediphosphate glucose.