Thermal transitions of myosin and its helical fragments. Regions of structural instability in the myosin molecule

Abstract

The structural stabilities of all the familiar proteolytic fragments of myosin were investigated in melting studies over the pH range 5.5-7.0 in 0.5 M KCl. All fragments except subfragment 2 undergo a melting transition manifested by the cooperative uptake of protons in the temperature range 34-47.degree. C, and these fragments experience an increase in transition temperature, Tm, as the pH is increased. Subfragment 2 undergoes a melting transition in the 43-55.degree. C range, manifested by the dissociation of protons, and it experiences a decrease in Tm as the pH is increased. pH changes can apparently modulate the relative stabilities of the light meromyosin, subfragment-1 and subfragment-2 regions of the myosin molecule.