R 24 571: A potent inhibitor of calmodulin-activated enzymes

R 24 571, a derivative of the antimycotic miconazole, is a very potent inhibitor of several Ca²⁺-calmodulin-dependent enzymes. Depending on the concentration of calmodulin, the I₅₀-values range from 0.5 ? 1.0 × 10^?8 M for brain phosphodiesterase to 1.5 ? 3.5 × 10^?7 M for erythrocyte Ca²⁺-ATPase and 5.0 × 10^?6 M for phosphorylase b kinase. Being much more potent, and devoid of affinity towards several receptors, R 24 571 is proposed as a more specific and useful tool for studying the involvement of calmodulin in biological processes than the currently used compounds.