| Popis: |
The rates of epimerization of UDP-[4-3H]glucose, UDP-[4-3H]galactose, and UDP-[4-3H]xylose with UDP-galactose 4-epimerase from Escherichia coli and that of UDP-[4-3H]glucuronate with UDP-galacturonate 4-epimerase from Anabaena flos-aquae were determined. In all cases the initial rates with the tritiated substrates were approximately one-half those of the corresponding nontritiated species. No isotope discrimination was observed at equilibrium. In analogy to the epimerization of UDP-galactose and UDP-glucose, for which a 4-keto intermediate has been directly demonstrated, the data suggest that corresponding intermediates are also formed during epimerization of UDP-xylose to UDP-l-arabinose and of UDP-glucuronate to UDP-galacturonate. |
