Lipid peroxidation of microsomal and mitochondrial membranes extracted with n-pentane and reconstituted with ubiquinol, dolichol and cholesterol.

ABSTRACT

Microsomes and mitochondria prepared from rat liver were extracted with n-pentane, a procedure which does not denature enzyme proteins. Protein and phospholipid were not extracted, but 75-80% of the total dolichol, 80-100% of the ubiquinone and 85-95% of the cholesterol were removed from both organelles by this procedure. Enzymatic and non-enzymatic lipid peroxidation in microsomes and non-enzymatic peroxidation in mitochondria were strongly inhibited when ubiquinol was reinserted into n-pentane-extracted membranes. When reconstitution with dolichol was performed, lipid peroxidation was increased or unchanged, while cholesterol decreased this activity in a concentration-dependent manner. In reconstitution experiments ubiquinol and dolichol together were less inhibitory than ubiquinol alone, whereas cholesterol accentuated the inhibitory effect of ubiquinol. Reconstitution with dolichols of different lengths, dolichyl esters or with alpha-unsaturated polyprenols further demonstrated that dolichol is not an antioxidant. It appears that mevalonate pathway lipids influence lipid peroxidation in membranes by modifying the properties of the bilayer.