Uridine Phosphorylase from Escherichia coli. Physical and Chemical Characterization

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Abstract
Uridine phosphorylase [EC 2.4.2.3] from E. coli was purified to homogeneity. The enzyme had a MW of 176,000 and consisted of 8 probably identical subunits with MW of 22,000. These numbers were determined from equilibrium centrifugations in the analytical ultracentrifuge, from dodecylsulfate gel electrophoresis and from amino acid analysis. The following physico-chemical constants were determined: .**GRAPHIC**. [sedimentation coefficient] = 8.2 .times. 10-13 S, v2 [partial specific volume] = 0.751 cm3/g, .**GRAPHIC**. (1 cm) = 6.73 and a specific activity of 183 units/mg towards uridine. The enzyme shows some activity towards deoxyuridine and thymidine. The activity is not impaired through substitution by bromo, fluoro or methyl groups in the 5-position of the uracil base, but no enzymatic activity is observed when cytosine base is used in the nucleoside substrate.