Interaction of trifluoperazine with porcine calmodulin F NMR and induced CD spectral studies

We have used ¹⁹F NMR and CD spectra to study interactions of TFP with CaM under various conditions where no aggregation of TFP occurs. It was found that TFP is bound to CaM in the absence of Ca²⁺ with K_a >4 × 10⁴ M in terms of ¹⁹F NMR of TFP and that KCl markedly influences the interaction of TFP with CaM. It was also found that TFP causes quite strong induced CD bands corresponding with the absorption bands of the aromatic ring of TFP when TFP is bound to Ca²⁺ -CaM. The induction of the CD bands was time-dependent and was composed of fast and slow phases.