The effect of choline deficiency on the activity of a phosphatidylcholine-requiring enzyme: Activity and properties of UDP-glucuronyltransferase in choline-deficient rats

The effect of choline deficiency on the kinetic properties of the microsomal enzyme UDP-glucuronyltransferase (EC2.4.1.17) was investigated in rats. Animals fed choline-deficient diets, as compared with animals fed a choline-replete diet or standard laboratory chow, showed almost a three-fold increase in enzyme activity when the enzyme was assayed at physiological concentrations of UDP-glucuronic acid (0.25 mM). The increase in activity appeared to be due to an enhanced affinity of the enzyme for UDP-glucuronic acid rather than to an increase in the amount of enzyme. These data indicate that the kinetic properties of tightly bound membrane enzymes are altered by a dietary change that is known to cause liver disease in the rat.