[33]Synthesis and properties of CAPP1-calmodulin

This chapter discusses the synthesis and properties of CAPP1-calmodulin. Covalent attachment of 1 mole of phenothiazine to 1 mole of calmodulin with norchlorpromazine isothiocyanate yields a phenothiazine-calmodulin adduct (CAPP1-calmodulin), which binds specifically, and with high affinity, to all calmodulin target proteins tested. CAPP1-calmodulin behaves as an antagonist of the stimulation of cAMP phosphodiesterase and myosin light chain kinase by calmodulin; it is a full agonist for the activation of phosphorylase kinase, glycogen synthase kinase, bacterial adenylate cyclase, and the Ca2+, Mg2+-ATPase; in the case of the calmodulin-stimulated protein phosphatase (calcineurin), it is a partial agonist. Thus CAPP1-caimodulin is a tool that can be used to identify calmodulin-regulated enzymes or function and to further the understanding of the interaction of calmodulin with its many target proteins. CAPP1-calmodulin preserves one of its phenothiazine sites, which allows it to bind phenothiazines and all calmodulin-regulated enzymes tested so far in a Ca2+-dependent manner. Two other covalent phenothiazine-calmodulin adducts, each of which contains two phenothiazines per mole of calmodulin, lose their biological activity.