Activation of Plant and Animal Calmodulin-Dependent Enzymes by Plant, Animal, Protist, and Fungal Calmodulins

Abstract

The activities of the calmodulin-dependent enzymes, pea seedling NAD kinase, bovine brain cyclic nucleotide phosphodiesterase and human erythroctye Ca²⁺-ATPase were determined in the presence of varying amounts of calmodulins from bovine brain, human erythrocyte, mung bean seed, sea pansy (a marine coelenterate), mushroom, and Tetrahymena. Pea seedling NAD kinase required 10 to 100-fold lower calmodulin concentration for 50% activation than did bovine brain cyclic nucleotide phosphodiesterase or human erythrocyte Ca²⁺-ATPase. The activation of phosphodiesterase and Ca²⁺-ATPase by all calmodulins tested was cooperative with Hill coefficients ranging from 1.3 to 2.0. The activation of NAD kinase by mushroom, Tetrahymena, sea pansy, bovine brain, and human erythrocyte calmodulin was not cooperative (Hill coefficients = 1.0) whereas activation of this enzyme by mung bean calmodulin was cooperative (Hill coefficient 1.3). The order of potency of the six calmodulins differed for each of the three enzymes. For Ca²⁺-ATPase the order of potency was erythrocyte > brain = sea pansy = mung bean = mushroom = Tetrahymena. For phosphodiesterase the order was erythrocyte = brain > mung bean = sea pansy > Tetrahymena > mushroom. For NAD kinase the order was Tetrahymena > mung bean > erythrocyte > brain = sea pansy = mushroom. These data show that calmodulin-dependent enzymes recognize different features of calcium-calmodulin complexes.