Mastoparan binding induces a structural change affecting both the N‐terminal and C‐terminal domains of calmodulin

113Cd-NMR studies of solutions of cadmium-loaded calmodulin (Cd4CaM) and the tetradecapeptide mastoparan in different ratios show that mastoparan binds to Cd4CaM with high affinity. The off-rate of protein- bound mastoparan is found to be 40 s-1 or less. The binding of one molecule of mastoparan to Cd4CaM is observed to affect all four metal-binding sites, indicating that both the N-terminal and C-terminal globular domains of the protein undergo conformational changes.