Incorporation of delta 5 desaturase substrate (dihomogammalinolenic acid, 20:3 n-6) and product (arachidonic acid 20:4 n-6) into rat liver cell nuclei.

The incorporation of [1-(14)C]20:3 n-6 and its desaturation product, [1-(14)C]20:4 n-6 into nuclear lipids from rat liver cells were investigated during in vitro delta5 desaturation. [1-(14)C]20:3 n-6 activated as 20:3 n-6-CoA by nuclear long chain acyl-CoA synthetase was: (1) incorporated into nuclear lipids mainly esterified to phospholipids and in a lesser proportion, to triglycerides and diglycerides; and (2) desaturated to 20:4 n-6-CoA by the nuclear delta5 desaturase. The amount of [1-(14)C]20:4 n-6 acid synthesized in cell nuclei increased along with time and was stimulated by the cytosol fraction. The major proportion of 20:4 n-6 was found in phospholipids and in a lesser proportion it remained as free fatty acids and was esterified to triglycerides and diglycerides. 20:4 n-6-CoA was incorporated into nuclear lipids and hydrolyzed to free fatty acid. These results indicate that liver cell nuclei possess the necessary enzymes to incorporate the delta5 desaturase substrate (20:3 n-6) as well as the product of desaturation (20:4 n-6) into nuclear TG, DG and PL following an acyl-CoA dependent pathway.