Isolation of a Stearoyl CoA Desaturase from Tetrahymena thermophila

Cell free preparations of Tetrahymena thermophila contain an enzyme that catalyzes the direct desaturation of stearoyl CoA to octadecenoic acid. The enzyme is associated with the microsomal fraction of the ciliate. Substrate for the enzyme consists of either free stearic acid or stearoyl CoA. Both ATP and CoA are required when free stearate is the substrate and are also highly stimulatory when stearoyl CoA is the substrate. With stearoyl CoA as the substrate, either NADH or NADPH are required for desaturase activity. In the presence of ATP and CoA, either NAD or NADP can replace NADH and NADPH. Desaturase activity is optimal when the enzyme is incubated at a pH of 7.2 and a temperature of 30–35°C. Highest levels of the stearoyl CoA desaturase are found in stationary phase ciliates grown at 35°C.