DIFFERENTIAL-EFFECTS OF FATTY-ACID AND PHOSPHOLIPID ACTIVATORS ON THECATALYTIC ACTIVITIES OF A STRUCTURALLY NOVEL PROTEIN-KINASE FROM RAT-LIVER

The lipid responsiveness of the structurally unique protein kinase, re ferred to as PAK-1, recently isolated from rat liver [(1994) J. Biol. Chem. 269, in press], is characterised by the high sensitivity (low mi cromolar) of its ribosomal S6(229-239) peptide kinase activity to both cardiolipin and the eis-unsaturated fatty acids and insensitivity to phosphatidylserine. Autophosphorylation of PAK-1 exhibited even greate r sensitivity (submicromolar) to cardiolipin, but was relatively less affected by phosphatidylserine. Oleate, the most potent activator of P AK-1's peptide kinase activity was relatively ineffectual with autopho sphorylation. These and other unusual characteristics, including high levels of basal catalytic activities, suggest a novel mechanism of reg ulation distinct from that of the protein kinase Cs