The mechanism of protein kinase C activation

Protein kinase C (PKC) consists of a family of closely related enzymes highly concentrated in the CNS. These enzymes respond to the second messengers calcium (Ca2+) and diacylglycerol (DAG), to express their activities at membrane locations. Each member of this enzyme family displays distinct biochemical characteristics and is enriched in different cellular and subcellular locations. Activation of PKC in the nervous system has been implicated in the regulation of neurotransmitter release, ion channels, growth and differentiation, and neural plasticity. It is believed that an increase in the intracellular concentration of Ca2+ triggers the association of a group of PKC isozymes with the membrane where DAG interacts with PKC to stimulate the enzyme activity. Stimulation of PKC at the cellular membrane is, therefore, dependent upon the duration and magnitude of the DAG signal. The association of PKC with the membrane may also lead to a conversion of the enzyme into an effector-independent form for a sustained activation after the Ca2+ and DAG signals dissipate. Activation of PKC results in the phosphorylation of cellular proteins; however, the physiological substrates of this enzyme in the nervous system are still poorly characterized.