FATTY ACID DELTA-5 DESATURATION IN RAT-LIVER CELL-NUCLEI

Activity of one of the key enzymes involved in arachidonic acid (20:4 n-6) biosynthesis, the Delta 5 desaturase, was found in rat liver cell nuclei. Up to now, it has been shown that the fatty acid desaturases are located exclusively in the endoplasmic reticulum. Similarly to wha t happens with microsomal enzyme the nuclear Delta 5 desaturase enzyme was only fully active in the presence of a cytosolic factor. In this condition it reached a specific activity of 50 pmol 20:4 n-6 formed/mi n/mg of protein. This fact would imply that purified nuclei like purif ied microsomes lack a soluble cytosol factor necessary for the total d esaturation reaction expression. Besides the nuclear Delta 5 desaturas e has an optimal pH of 7.6 and is inhibited by 1 or 10 mM KCN. Low lon g chain acyl-CoA synthetase activity that catalyzes the formation of 2 0:3 n-6-CoA, was also found in liver nuclei. This step would be essent ial in nuclear desaturation since when ATP and/or CoA (necessary for t he acylation reaction) are omitted from the incubation mixture, the de saturation reaction does not take place.