A FLUORESCENCE TEMPERATURE-JUMP STUDY ON CA-2+-INDUCED CONFORMATIONAL-CHANGES IN CALMODULIN

Calmodulin has been shown to alter its conformation so as to interact with a number of target proteins upon Ca2+ binding. A Ca2+-binding study of calmodulin was performed by monitoring the fluorescence of intrinsic tyrosine residues and the probe 1-anilinonaphthalene-8-sulfonate (ANS). ANS fluorescence was shown to reflect Ca2+ binding to both high- and low-affinity sites. On the one hand, tyrosine fluorescence was sensitive only to the high-affinity Ca2+ binding. Temperature-jump investigation of the ternary complex of Ca2+-calmodullin-ANS in combination with monitoring of ANS fluorescence demonstrated the kinetic characteristics of the conformational change. The relaxation process was attributed to Ca2+-induced conformational change and the rate constants of this process were evaluated. On the basis of the rate constants of the conformational change, a rapid response of calmodulin in Ca2+ signaling is suggested. © 1990.