Fluorescence spectra studies on the interaction between lanthanides and calmodulin

The conformation of Calmodulin (CaM) induced by lanthanides has been examined using fluorescence methods. With the addition of lanthanide (Ln
³⁺
), the intrinsic fluorescence intensity of CaM without calcium ions (Apo-CaM) first increases and then decreases. Ln
³⁺
causes the decrease of intrinsic fluorescence intensity of calcium saturated CaM (Cat-CaM) only at high concentrations. At low concentrations, Ln
³⁺
results not only in the enhancement of fluorescence intensity of Apo-CaM, but also in a blue shift of the maximum emission wavelengh of dansyllabeled calmodulin (Apo-D-CaM). The molecular mechanism of the interaction between Ln
³⁺
and CaM has been discussed in the light of the fluorescence spectra.