[Kinetic cooperation in inhibition of protein kinase C by diene conjugates of phospholipids and arachidonic acid in vitro].

The changes in the rabbit heart protein kinase C activity induced by phospholipids (phosphatidylserine, phosphatidylethanolamine, phosphatidylinositol) and arachidonic acid were studied. It was shown that diene conjugates, which reflect the degree of effector oxidizability, inhibit the enzyme. A positive kinetic cooperativity of the enzymatic reaction towards the inhibitors (diene conjugates) was found. The Hill coefficients for phospholipids and arachidonic acid are 1.75 and 4.0, respectively. It was found that the Hill equation for the inhibitors is true in the case of phospholipids and nonexistent in the case of arachidonic acid. Using arachidonic acid as an example, it was demonstrated that it increase in cooperativity, i.e. eta H, is associated with changes in the oxidizability within a very narrow range (from 15% to 22%). It was found also that the protein kinase C affinity for phospholipid diene conjugates is different. For phosphatidylethanolamine and phosphatidylinositol the binding affinity is two times as high as that for phosphatidylserine, i.e., 10-15 times as high as that for arachidonic acid diene conjugates. It is concluded that protein kinase C belongs to the family of peroxy lipid-dependent enzymes that are highly sensitive to lipid peroxidation products.