Kinetics of conformational change of troponin C induced by calcium

The kinetics of conformational change of troponin C (TN-C) induced by binding and removal of calcium ions were studied by measuring the fluorescence of tyrosine by stopped-flow spectrofluorometry. When the concentration of free calcium ions in the solution [Ca2+] was increased rapidly from 4X10(-9)M to 1X10(-3)M at neutral pH, a first-order reaction with a rate constant of 13.7 sec-1, which was preceded by a much faster reaction, was observed. In contrast, when [Ca2+] was reduced from 2X10(-3)M to 4.4X10(-8)M, two first-order reactions with rate constants of 7.4 and 0.78 sec-1, preceded by a much faster reaction, were observed.