Fatty acid desaturase system of yeast microsomes: Involvement of cytochrome b5-containing electron-transport chain

Abstract

The oxidative desaturation of palmitoyl CoA by microsomes from anaerobically grown Saccharomyces cerevisiae has been studied by using NADH as electron donor. The desaturation product was identified as palmitoleic acid by periodate oxidation. The desaturase activity was sensitive to relatively high concentrations of cyanide; the concentration of cyanide causing half-maximal inhibition was determined to be 7.1 m m. The rate of reoxidation of cytochrome b 5 in NADH-reduced microsomes was stimulated by the addition of palmitoyl CoA, and the amount of cytochrome b 5 reoxidized by the palmitoyl CoA added could be closely correlated to the amount of palmitoleate formed. No stimulation of the reoxidation of cytochrome b 5 was induced by palmitoyl CoA in microsomes prepared from the desaturase-repressed cells and from a desaturase-deficient mutant, strain KD-20. It is concluded that the fatty acyl CoA desaturase system of yeast microsomes involves cytochrome b 5 as an electron carrier and that the terminal desaturase is sensitive to relatively high concentrations of cyanide.