Abstract: Plant extracellular calmodulin(CaM) has been purified from cauliflower and identified with NADkinase(NADK) activation and inhibition effect of CaMantagonist W7. Tb³⁺ fluorescence titration showed that extracellular CaMcontained four metal-binding sites. The excitation spectrum and emission specturm indicated that extracellular CaMcontained one tyrosine residue which could transfer energy to bound Tb³⁺ . Based on Förster type nonradiative energy transfer theory, the distances of Tyr→sites Ⅲ, Ⅳ have been determined, these are 1.104 nm(Tyr→Ⅲ, site) and 1.056 nm(Tyr→Ⅳ, site). By studing the effect of CaMantagonist W7 and CaMantibody on Tb³⁺ sensitized fluorescence, it was found that the binding sites of W7 and antibody were located on the c terminal part of plant extracellular CaMwhich contains domain Ⅲ and domain Ⅳ.

Key words: Extracellular calmodulin, Lanthanide luminescence probe, Terbium(Ⅲ), CaM antagonist