The effect of isomeric trans-18:1 acids on the desaturation of palmitic, linoleic and eicosa-8,11,14-trienoic acids by rat liver microsomes.

The inhibitory effects of the positional isomers of trans-18:1 acids on the desaturation of palmitic acid to palmitoleic (delta 9-desaturase), linoleic to gamma-linolenic (delta 6-desaturase) and eicosa-8,11,14-trienoic to arachidonic acid (delta 5-desaturase) were investigated. These trans-18:1 acids were found to be inhibitory for the microsomal delta 6-, delta 9- and delta 5-desaturases of rat liver. The position of the double bond in the trans-18:1 acids seems to be important in determining the degree of inhibition. At inhibitor/substrate ratio of 3:1, the delta 6-desaturase was most strongly inhibited by trans-delta 3, -delta 4, -delta 7 and -delta 15-18:1 isomers, whereas the delta 9-desaturase was most strongly inhibited by trans-delta3, -delta 5, -delta 7, -delta 10, -delta 12, -delta 13 and -delta 16 isomers. At inhibitor/substrate ratio of 6:1, the delta 5-desaturase was most strongly inhibited by delta 3-, delta 9-, delta 13- and delta 15-isomers. When 18:0 was added to the incubations of 16:0, 18:2 and 20:3 at the same I/S ratios used for the trans-18:1 acids, weak inhibition for delta 9- desaturase and no inhibition for delta 5- and delta 6-desaturases was observed.