Apparent kinetic constants of the wild-type and mutant enzymes were determined in membrane fraction of recombinant yeast cells toward UDP-glucuronic acid by varying its concentration (0.025–5.0 mM) while that of 4-MU was kept constant (1.0 mM). Similarly, the apparent kinetic constants toward 4-MU were calculated by varying its concentration (0.01–2.0 mM) for a fixed concentration in UDP-glucuronic acid (5.0 mM). K _m,V _max, and the catalytic efficiencyV _max/K _m were expressed as micromolar concentration, nanomoles per minute per milligram of protein, and liters per minute per milligram of protein, respectively.