Calcium stimualtion of protein kinase C in the absence of added phospholipids

The activity of protein kinase C as isolated and described by Inoue, M., Kishimoto, A., Takai, Y., and Nishizuka, Y. (1977) J. Biol. Chem. $\text{252}$, 7610–7616, can be markedly stimulated by Ca²⁺ in the presence of 4 mM Mg²⁺. This Ca²⁺ dependency does not require the presence of phospholipids or exogenous calmodulin. The increase in activity in the presence of Ca²⁺ is blocked by fluphenazine in the presence of 30 mM 2-mercaptoethanol. These results suggest that a calmodulin-like moiety may be a subunit of prokinase C.