KINETICS OF FOLDING OF THE MYOSIN ROD

The kinetics of the unfolding and refolding of the myosin rod have bee n studied by fluorescence and circular dichroism techniques, at differ ent concentrations of protein and guanidine hydrochloride. The unfoldi ng of the myosin rod was fast and at least biphasic in 2-3 M denaturan t, with an initial immediate phase followed by a slower low-amplitude first-order phase. The refolding of the rod in 0.4-2 M guanidine hydro chloride was also at least biphasic; an initial immediate phase preced ed a slow second-order phase. At the final denaturant concentration of 0.8 M, the amplitude of the burst phase was weakly dependent on the p rotein concentration and the rate constant of the refolding slow phase was optimal. These data are incorporated into a folding mechanism wit h at least three states. The high rates of the first steps of unfoldin g and refolding may be relevant for the functioning of the native myos in molecule by allowing a transient separation of the two strands of t he myosin tail.