Effect of local anesthetics on stearoyl-CoA desaturase of Tetrahymena microsomes.

The effect of local anesthetics on the stearoyl-CoA desaturase activity was studied using Tetrahymena microsomal preparation. Dibucaine, tetracaine, and propranolol, a beta-blocking agent, nonspecifically inhibited the activities of NADPH-ferrihemoprotein reductase as well as of stearoyl-CoA desaturase and the terminal component, but lidocaine and procaine had no effect on these activities. The inhibitory potency was decreased in the order of dibucaine greater than propranolol greater than tetracaine much greater than lidocaine = procaine. According to the double-reciprocal plots of stearoyl-CoA desaturase, the inhibition by dibucaine appeared to be noncompetitive with respect to stearoyl-CoA as substrate. However, the activity of NADH-ferricyanide reductase was not significantly affected by concentrations of propranolol and tetracaine lower than 10mM, but by dibucaine. The terminal component, cyanide-sensitive factor, was most sensitive to local anesthetics among the microsomal electron transport components, suggesting a rate-limiting enzyme.