Pancreatic phospholipase A2 is not regulated by calmodulin

It was previously suggested [Wong, P.Y.-K and Cheung, W.Y. (1979) Biochem. Biophys. Res. Comm. $\text{90}$, 473–480] that the Ca²⁺ activation of phospholipase A₂ is mediated by the calcium binding protein calmodulin. In the present study phospholipase A₂ from pig pancreas was shown to be absolutely Ca²⁺ dependent but the enzyme was not stimulated by exogenous calmodulin and no endogenous calmodulin was found in the preparation. The enzyme was inhibited in the absence of calmodulin by several drugs (trifluoperazine, mepacrine, promethazine and propranolol) which are known to bind to calmodulin. A kinetic analysis indicated that trifluoperazine competitively inhibited phospholipase A₂, probably by interacting with phospholipid substrate.