Synthesis and metabolism of arachidonyl- and eicosapentaenoyl-CoA in rat aorta.

In studies on the metabolism of polyunsaturated fatty acids, acyl-CoA synthetase for 5,8,11,14-20:4 (arachidonic acid) and 5,8,11,14,17-20:5 (eicosapentaenoic acid) and the incorporation of these fatty acids into complex lipids and their conversion to CO2 were investigated in rat aorta. The activity of acyl-CoA synthetase was 35.9 for arachidonic acid and 63.0 for eicosapentaenoic acid (nmol/mg protein per 10 min) and the apparent Km values were 45 microM for arachidonic acid and 56 microM for eicosapentaenoic acid. Inhibition of eicosapentaenoyl-CoA synthesis by arachidonic acid was stronger than that of arachidonyl-CoA synthesis by eicosapentaenoic acid. Arachidonic acid and eicosapentaenoic acid were mostly incorporated into phospholipids. The incorporation of these fatty acids into cholesterol ester and their conversion to CO2 were less than those of palmitic acid, but their incorporation into triacyglycerol was greater. The incorporation of these fatty acids into phosphatidylserine + phosphatidylinositol and phosphatidylethanolamine was also greater than that of palmitic acid. The patterns of incorporation of arachidonic acid and eicosapentaenoic acid were similar. The physiological roles of these polyunsaturated fatty acids and the interference of eicosapentaenoic acid in arachidonic acid metabolism are discussed on the basis of these results.