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Three types of protein kinase C were purified from rabbit brain cytosol. Each type has a molecular mass of approximately 80 kDa and serves as a receptor for phorbol esters. Polyclonal antibodies produced to two protein kinase C types were relatively type-specific, indicating that these proteins have unique antigenic determinants. We, therefore, characterized the enzymatic activities to determine if these proteins also had distinct biochemical properties. Type 1 protein kinase C was relatively less Ca2+-dependent than types 2 and 3. The addition of Ca2+ increased Vmax approximately 40% for type 1,600% for type 2, and 1400% for type 3 as compared to the Vmax measured at lower Ca2+ conditions. These results suggest that differences in primary structure can confer type-specific biochemical properties, and this in turn may provide the basis for protein kinase C type-specific stimulus-response coupling.
Jaken et al. (Wed,) studied this question.