Evidence for the presence of the stearyl-CoA desaturase system in the sarcoplasmic reticulum of rabbit slow muscle.

We have shown that the isolated sarcoplasmic reticulum from rabbit slow muscle contains cytochrome b5 which can be reduced via a flavoprotein, with FAD as the prosthetic group. In the presence of NADH and oxygen, these sarcoplasmic reticulum membranes can convert stearyl-CoA to oleyl-CoA, similarly to liver endoplasmic reticulum membranes. However, the stearyl-CoA desaturase system is virtually lacking in fast muscle sarcoplasmic reticulum. The data suggest that these differences between fast and slow twitch muscle may be related to the characteristic fatty acid composition of phospholipids and the function of the sarcoplasmic reticulum.