Activation of Protein Kinase C with Cardiolipin-Containing Liposomes in Relation to Membrane-Protein Interaction

Abstract

Many cytoplasmic proteins, including Ca²⁺-and phospholipid-dependent protein kinase (protein kinase C) of polymorphonuclear leukocytes (PMNs) associate in Ca²⁺-dependent manner with phospholipid liposomes containing cardiolipin (CL), as in the case of phosphatidylserine (PS)-con-taining liposomes. A crude protein kinase C fraction was purified by association of the enzyme with CL-containing liposomes (flotation method). The partially purified protein kinase C from rat brain or guinea pig PMN was activated by the CL-containing liposomes in the presence of dioleoylglyc-erol (DG) and Ca²⁺. This activation was analogous to that of PS. The half maximum activity was obtained with 20 μM CL in the presence of 1μM Ca²⁺ and 5μM DG. Many of the cytoplasmic proteins which associate with CL-containing liposomes were preferentially phosphorylated by membrane-associated protein kinase C in the presence of DG and Ca²⁺. These results suggest that the association of cytoplasmic protein kinase C with the membrane has an important role in regulation of protein kinase C activity in relation to the association of other cytoplasmic proteins to the membrane.