Stearyl coenzyme A desaturase activity in mouse liver microsomes of varying lipid composition

Liver microsomes derived from mice fed fat-free diets contained tenfold more stearyl coenzyme A desaturase activity than microsomes derived from mice fed a safflower oil supplemented diet. Removal of the native lipid from each of the microsomal desaturase proteins was performed and the native lipid was replaced by a mixture of phosphatidylcholine and oleic acid. Desaturase activity could only be restored to the level present in the original microsomes in both instances and it was concluded that, although the lipid composition of the two kinds of microsomes was markedly different, this was not directly responsible for the difference in enzyme activity. Microsomal electron transport chain intermediates remained unchanged during the feeding time tested, however, the rate of oxidation of cytochrome b 5could be stimulated sevenfold by stearyl coenzyme A only in microsomes that contained a high desaturase activity. This demonstrates that a blockage in the electron transport chain exists in microsomes from mice fed safflower oil supplemented diets and that this correlates with a markedly reduced desaturase activity in these microsomes.