Autophosphorylation of plasma membrane bound calcium calmodulin dependent protein kinase from pea seedlings and modification of catalytic activity by autophosphorylation.

We have previously shown that pea seedling plasma membrane contains a protein kinase whose activity towards plasma membrane proteins is markedly increased by micromolar concentrations of calcium and calmodulin. The evidence in this paper suggests that this protein kinase autophosphorylates, that autophosphorylation is increased in a calcium and calmodulin dependent fashion and that prior autophosphorylation modifies activity towards an exogenous substrate. This protein kinase has a molecular weight of approximately 18,000 and is referred to as phosphoprotein18 (pp18).