Direct activation of purified protein kinase C by unsaturated fatty acids (oleate and arachidonate) in the absence of phospholipids and Ca²⁺

Unsaturated fatty acids (oleic acid and arachidonic acid) activate purified protein kinase C independently of phospholipid and Ca²⁺. Oleic acid activation of protein kinase C is as effective as phosphatidylserine and Ca²⁺. K_a, values for oleic acid and arachidonic acid are 50 and 53 μM, respectively. In contrast to the cis fatty acids, a trans form (elaidic acid) or a saturated fatty acid (stearic acid) has little or no effect on protein kinase C activation. If cis fatty acid liberation is physiologically important, this suggests that another mechanism may exist for protein kinase C activation, in addition to phospholipase C/phosphatidylinositol turnover signaling, possibly via the liberation of cis fatty acids by the Ca²⁺-dependent phospholipase A₂ system.