Differential scanning calorimetric study of muscle and its proteins: Myosin and its subfragments

Abstract

Abstract The thermal denaturation of rabbit skeletal muscle myosin and its subfragments was investigated by differential scanning calorimetry. The thermal denaturation of myosin was shown to occur via three (at least) partly independent cooperative endothermic processes. The temperatures at which these processes occurred (312, 317 and 323 K at pH 6.0 and I=1.0) were shown to vary with pH (5.5–8.0) and I (0.05–1.0). The apparent enthalpy of denaturation of myosin was also shown to be dependent on pH and I. By comparing thermograms of myosin with those of the isolated myosin subfragments, the three major processes associated with the thermal denaturation of rabbit myosin could be tentatively assigned to different regions of the myosin molecule, namely, the helical tail, the ‘hinge‐region’ and the globular heads. The ‘hinge‐region’ thermal denaturation was shown to be reversible at pH 6.0 and I=1.0. Investigations of the effects of ortho‐, pyro‐, and tripolyphosphate on the thermal denaturation of myosin showed that added pyrophosphate destabilised the myosin molecule by about 9 K compared to the effects of ortho and tripolyphosphate, even though the latter was probably hydrolysed to ortho and diphosphate.