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 No activity with UDP-Galactose, UDP- Glucose or UDP-Xylose. Optimum pH is 7.9. Active from pH 6 to 8.9. Homodimer. In roots, leaf veins, siliques, flowers, pollen and stems. Belongs to the NAD(P)-dependent epimerase/dehydratase family.