Inhibition of desaturation of palmitic, linoleic and eicosa-8,11,14-trienoic acids in vitro by isomeric cis-octadecenoic acids.

The effects of the positional isomers of cis-18 : 1 acids on the desaturation of 18 : 2 omega 6 leads to 18 : 3 omega 6 (delta 6 desaturase), 20 : 3 omega 6 leads to 20 : 4 omega 6 (delta 5 desaturase) and 16 : 0 leads to 16 : 1 (delta 9 desaturase) were investigated using essential fatty acid deficient rat liver microsomes. The isomeric cis-18 : 1 acids were found to be inhibitory for the delta 6, delta 5 and delta 9 desaturases, and the position of the double bond is important in determining the degree of inhibition. The effects of the several cis-18 : 1 isomers on delta 6 and delta 5 desaturases were parallel in magnitude exept for the cis-delta isomer which gave 17.5% inhibition for delta 6 desaturase and no inhibition for delta 5 desaturase. The strongest inhibitor for delta 6 desaturase (cis-delta 8 18 : 1) was also the most potent inhibitor for delta 5 desaturase, and the weakest inhibitor for delta 6 desaturase (cis-delta 3 18 : 1) was the least effective inhibitor on delta 5 desaturase. The delta 9 desaturase was maximally inhibited by cis-delta 10 and delta 11 18 : 1 isomers. The cis-18 : 1 acid isomers in partially hydrogenated edible fats may have effects on the lipid metabolism through their inhibitory effects on the desaturases.