Abstract
43Ca NMR spectra of Ca 2+- Tetrahymena calmodulin( Tet. CaM.) complexes have been observed under various conditions. Off-rate of Ca 2+ from Tet. CaM. is estimated to be approx. 2.7 × 10 3 s −1 under a certain assumption. Relaxation rates of 43Ca NMR of Ca 2+- Tet. CaM. are remarkably increased(by one order in magnitude) by adding trifluoperazine(TFP), a potent calmodulin antagonist. Relaxation parameters estimated suggest that Ca 2+ mobility is reduced by the TFP binding. A stoichiometry of TFP is two moles per Tet. CaM. molecule. The relaxation rates of 43Ca NMR signals are increased by adding excessive Mg 2+ to the Ca 2+- Tet. CaM. solutions. The addition of Mg 2+ to the Ca 2+- Tet. CaM. complex decreases apparent pKa value of the complex as well.
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