Purification and characterization of UDP-galactose-4-epimerase from bovine tissues

Bovine liver and mammary UDP-galactose-4-epimerases have been purified to apparent electrophoretic homogeneity by a simple procedure involving the use of two affinity adsorbants, UDP-hexanolamine-Sepharose and NAD+-hexanolamine-Sepharose. The bovine thyroid epimerase has been partially purified by the same procedure. All three enzymes require NAD+ for activity, and all have a similar apparent molecular weight of approximately 40,000 as determined by gel filtration of the active enzymes. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the liver and mammary epimerases revealed similar molecular weights of 37,000 for both enzymes thus indicating that neither protein was dimeric. During development of the isolation procedure conditions were determined which would stabilize enzymatic activity in very dilute solutions. The liver and mammary enzymes, although similar in some respects, differed in amino acid composition and specific activity.