Isolation and identification of a novel cellular protein that potently activates Ca2+/phospholipid-dependent protein kinase (protein kinase C).

A novel heat-stable cellular protein that significantly stimulated Ca2+/phospholipid-dependent protein kinase (protein kinase C, PKC) was identified. It is ubiquitous and has a molecular mass of over 150 kDa, and was shown to be specific for PKC. It activates PKC in the absence and presence of phospholipids; however, its maximal stimulatory potential was achieved when optimal amounts of phospholipids were also present in the reaction medium. Thus, in comparison with classical cofactors such as phospholipid, where activation of PKC mainly involves interaction with the regulatory domain of PKC, the mechanism of activation of PKC by the activator appears to involve several binding sites.