Electron-transfer mechanism associated with fatty acid desaturation catalyzed by liver microsomes

Suitable assay conditions are described for the NADPH-dependent oxidative desaturation of stearyl-CoA by rat-liver microsomes.

NADH is an even more effective electron donor than NADPH. Ascorbate at high concentrations also acts as a donor, but with low efficiency. Unlike the NADPH-dependent drug hydroxylations, the desaturation reaction does not seem to involve the microsomal hemoprotein P-450. Instead, a hitherto unknown cyanide-sensitive factor appears to be involved in the desaturation mechanism, regardless of the electron donors employed. The microsomal NADPH-specific flavoprotein with a cytochrome $\text{c}$ reductase activity seems to participate, not only in the NADPH-dependent drug hydroxylations, but also in the NADPH-supported desaturation. Microsomal oxidation of methanol, which requires NADPH and is sensitive to cyanide, appears to be catalyzed by a mechanism which differs from that involved in desaturation.

On the basis of these findings the electron-transfer mechanisms associated with these microsomal reactions are discussed.