Coenzyme A-dependent modification of fatty acyl chains of rat liver membrane phospholipids: possible involvement of ATP-independent acyl-CoA synthesis

Certain species of fatty acyl chains of microsomal lipids from rat hepatocytes underwent desaturation when the microsomal fraction was incubated with GOA and NADH. For instance, 18:0, 18:2(n-6), and 20:3(n-6) incorporated into mem- brane lipids were gradually converted to 18:l(n-9), 18:3(n-6), and 20:4(n-6), respectively. Further, 20:5(n-3) and 18:3(n-6) were metabolized to 22:5(n-3) and 20:4(n-6), respectively, through chain elongation or chain elongation plus subsequent desaturation when malonyl-CoA was present. In contrast to esterified fatty acids, negligible change was observed for free fatty acids under the same experimental conditions. It is appar- ent that ATP-independent acyl-CoA synthesis is implicated in such enzymatic modification of fatty acyl chains. The presence of either gel-filtered cytosol or bovine serum albumin markedly potentiated the reaction. However, the addition of ATP and Mg2+ did not accelerate the overall reaction induced in the presence of GOA alone. These results suggest that the path- way