Differential effects of fatty acid and phosholipid activators on the catalytic activities of a structurally novel protein kinase from rat liver

Abstract

The lipid responsiveness of the structurally unique protein kinase, referred to as PAK‐1, recently isolated from rat liver [(1994) J. Biol. Chem. 269, in press], is characterised by the high sensitivity (low micromolar) of its ribosomal S6(229–239) peptide kinase activity to both cardiolipin and the cis‐unsaturated fatty acids and insensitivity to phosphatidylserine. Autophosphorylation of PAK‐1 exhibited even greater sensitivity (submicromolar) to cardiolipin, but was relatively less affected by phosphatidylserine. Oleate, the most potent activator of PAK‐1's peptide kinase activity was relatively ineffectual with autophosphorylation. These and other unusual characteristics, including high levels of basal catalytic activities, suggest a novel mechanism of regulation distinct from that of the protein kinase Cs