Purification of a Thymidine-diphospho-4-keto-6-Deoxy-D-Glucose Epimerase from an Erythromycin-Producing Strain of Saccharopolyspora erythraea

A thymidine-diphospho-4-keto-6-deoxy-D-glucose epimerase was purified from Saccharopolyspora erythraea, the producer of the macrolide antibiotic erythromycin, by a high resolution chromatographic method that exploited the difference in behavior of the protein on ion exchange columns at pH 7.5 and 5.5. By this procedure and by hydrophobic interaction chromatography, the enzyme was purified more than 400-fold to apparent homogeneity. The epimerase is a monomer of Mr 55,000, as determined by reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration. The apparent Michaelis-Menten kinetic constants were determined to be K′m of 120 μM and V′max of 0.38 μmol mg−1 min−1. Southern analysis indicates that this epimerase is encoded by a gene that is not located within the known confines of the erythromycin biosynthetic gene cluster.