Journal of Lipid Research, Vol 26, 819-823, Copyright © 1985 by Lipid Research, Inc.
Stimulation by unsaturated fatty acid of squalene uptake in rat liver microsomes
J Chin and K Bloch
Supernatant protein factor (SPF) and anionic phospholipids such as
phosphatidylglycerol (PG) stimulate squalene epoxidase activity in rat
liver microsomes by promoting [3H]squalene uptake as well as substrate
translocation (Chin, J., and K. Bloch. 1984. J. Biol. Chem. 259: 11735-
11738). This process is postulated to be membrane-mediated and not
carrier-mediated. Here we show that treatment of PG with phospholipase A2
in the presence of bovine serum albumin abolishes the stimulatory effect of
SPF on epoxidase activity. Disaturated fatty acyl-PGs are not as effective
as egg yolk lecithin PG in the SPF effect. These findings suggest an
important role for the unsaturated fatty acid moiety of PG. We also show
that at submicellar concentrations, cis-unsaturated fatty acids stimulate
microsomal epoxidase activity whereas saturated fatty acids do not. This
effect is due to an increase in substrate uptake which in turn may
facilitate substrate availability to the enzyme.