A calcium-dependent protein activator of mammalian cyclic nucleotide phosphodiesterase from Blastocladiella emersonii

Abstract

1. Introduction A heat-stable, acidic calcium-binding protein (PI 4.3), with mol. wt 18 920 and originally described as an activator of cyclic nucleotide phosphodiesterase [I], has been purified and characterized from a variety of mammalian tissues [2-51, as well as from electro- plax of the electric eel [6]. This protein has been shown to exhibit multiple calcium-dependent regula- tory activities, including activation of brain adenylate cyclase [7], human erythrocyte membrane (Mg” t Ca”)dependent ATPase [8], protein kinase [9] and other calcium-sensitive reactions [ 10,111. More recently, crude extracts of > 10 representative invertebrate species were examined and all were found to have the activator protein [ 121, referred to as calmodulin [ 11. Thus, calmodulin appears to be ubiquitous in the animal kingdom. Moreover, it lacks tissue and species specificity, suggesting that it may be a very primitive protein. However, the occurrence of such a protein in bacteria or lower eukaryotes has not been described. Here we report the occurrence, in cells of the phycomycete