SPECIFICITY OF UDP-GLUCOSE 4-EPIMERASE FROM YEAST SACCHAROMYCES FRAGILIS

1. 1. The reactivity of UDP-glucose 4-epimerase (EC 5.1.3.2) from the yeast Saccharomyces fragilis toward 11 analogs of UDPG has been examined. The compounds tested involve stereochemical modifications of the hexosyl and ribosyl moieties of UDPG. 2. 2. Of the 11 compounds only UDP-β-l-arabinose, UDP-d-fucose and UDP-d-xylose are epimerized. However, evidence is presented indicating that these epimerizations are due to contaminating enzymes and are not due to UDPG 4-epimerase. 3. 3. The substances UDP-d-mannose, UDP-N-acetyl-d-galactosamine, UDP-d-allose and UDP-3-O-methyl-d-glucose were not epimerized. These observations are in agreement with the hypothesis of Budowsky et al.9 since the postulated hexose: uracil hydrogen bond, which is necessary for enzyme action in their mechanism, would be hindered in these substances. 4. 4. dUDPG is not acted upon by the yeast epimerase. It has been reported to serve as a substrate for the epimerase from calf liver. 5. 5. Other substrates which were not epimerized are UDP-β-d-glucose, UDP-d-glucuronic acid, UDP-4-O-methyl-d-glucose, ADPG, CDPG, GDPG, IDPG and dTDPG. © 1968.