Kinetics of Conformational Change of Troponin-C Induced by Proton Binding or Removal in the Absence of Calcium Ions

Abstract
The kinetics of the conformational change of troponin-C induced by binding or removal of protons was studied by a stoppd-flow pH-jump spectrofluorometric method. In the pH-down experiment (to investigate the kinetics of conformational change from the deprotonated state to the protonated state), a single first-order reaction with a rate constant and amplitude of 1.75–2.4 sec−1 and around 10%, respectively, was observed. On the other hand, two firstorder reactions with rate constants of 0.84–1.6 sec−1 and 0.08–0.4 sec−1 were observed in the pH-up experiment, the total amplitudes of these reactions being around 10–20%. The pH dependences of the rate constants of these reactions were analyzed in terms of a three-species mechanism.

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