Three distinct forms of rat brain protein kinase C: differential response to unsaturated fatty acids.

Although the three distinct forms of protein kinase C isolated from rat brain soluble fraction are structurally very similar, they respond differently to free unsaturated fatty acids such as arachidonic acid to exhibit their catalytic activity. Type I enzyme encoded by gamma-sequence, as predicted by cDNA clone analysis, responds to these fatty acids only slightly, whereas Type III enzyme determined by alpha-sequence is activated by free unsaturated fatty acids in the presence of Ca2+ in a comparable manner to phosphatidylserine plus diacylglycerol. Type II, a mixture of two enzymes encoded by beta I- and beta II-sequence, resulting from alternative splicing, shows properties in between those of Type I and Type III. Some of these forms of protein kinase C may function at a relatively later phase of cellular responses when large amounts of unsaturated fatty acids and Ca2+ are mobilized.