Electron Transfer Mechanism Involved in Stearoyl-Coenzyme A Desaturation by Particulate Fraction of Mycobacterium phlei

The particulate fraction prepared from sonic extracts of Mycobacterium phlei catalyzes the desaturation of stearoyl-CoA in the presence of molecular oxygen, NADPH, and exogenous FAD; no requirement for ferrous ion is, however, detectable. Like the similar desaturase system of rat liver microsomes, theM. phlei system appears to contain a cyanide-sensitive factor as the terminal enzyme. Two types of NADPH-cytochrome c reductase activity are detectable in the particulate fraction; one is a weak activity which is independent of exogenous FAD and the other requires added FAD for activity. Similarities between the behavior of the FAD-requiring cytochrome c reductase activity and that of the overall desaturase activity toward KCl, HgCl2, Emalgen 911, etc. indicate the participation of this reductase activity in the desaturation system. The NADPH-ferricyanide reductase activity of the particulate fraction is not enhanced by exogenous FAD and its properties differ from those of the FAD-requiring NADPH-cytochrome c reductase activity in several respects. The soluble fraction of M. phlei also contains an FAD-requiring NADPH-cytochrome c reductase activity, but its properties are again different from those of its particulate counterpart. Based on these findings, the electron transfer mechanism involved in the stearoyl-CoA desaturase system of M. phlei is discussed.