The Activation of Brain Adenylate Cyclase and Brain Cyclic‐Nucleotide Phosphodiesterase by Seven Calmodulin Derivatives

Abstract

A comparison was made of the ability of 7 calmodulin derivatives to displace 125I-labeled [bovine pancreatic] calmodulin and to activate adenylate cyclase in a [rat] brain particulate fraction. The activation of [guinea pig] brain-soluble cyclic-nucleotide phosphodiesterase by the same calmodulin derivatives was examined in parallel. The dose for half-maximal inhibition of 125I-labeled calmodulin binding and the apparent Km of adenylate cyclase activation were comparable in brain membranes. These concentrations were 20-40 times higher than the corresponding apparent Km values of activation of cyclic-nucleotide phosphodiesterase. Modifying the single histidine residue or both tyrosine residues exerted no influence on the biological properties of calmodulin. The carboxymethylation of 2 methionine residues or the amidation of several carboxyl groups reduced the activation properties of calmodulin on adenylate cyclase and cyclic-nucleotide phosphodiesterase. Altering 7 lysine or 4 arginine residues caused 2 proteins whose activation properties on adenylate cyclase and phosphodiesterase were modified in a way suggesting that lysine and arginine residues are important in the interaction of native calmodulin with each enzyme.