Involved in the synthesis of the negatively charged monosaccharide that forms the backbone of pectic cell wall components. UDP-alpha-D-glucuronate = UDP-alpha-D-galacturonate Activated by glycerol, not effected by dimethyl sulfoxide and inhibited by high concentration of monovalent salts, UDP-xylose, UDP-arabinose or UDP. Equilibrium between UDP-glucuronate and UDP-D-galacturonate established at 1:1.9. No activity with UDP-Galactose, UDP-Glucose, UDP-arabinose, UDP-Xylose, CDP-glucose or GDP-manose. Optimum pH is 7.5. Active from pH 6.8 to 8.2. Active between 20 and 55 degrees Celsius. Homodimer. In roots, leaves, siliques, flowers, pollen and stems. Belongs to the NAD(P)-dependent epimerase/dehydratase family.