[Stages in the thermal denaturation of spiral fragments of myosin].

Scanning microcalorimetry is used to study heat denaturation of myosin "tail" helical fragments, light meromyosin and the LF-3 subfragment. It has been shown that all the data obtained were well explained by the existence of a set of quasi-independent cooperative regions. Probable location sites of separate cooperative regions in the helical part of the molecule are indicated. The obtained places of cooperative "breaks" are in a good agreement with the places of predominant cleavage of the myosin tail by proteolytic enzymes at its limited hydrolysis. The total denaturation enthalpy for each of the helical fragments per hydrogen bond at 100 degrees C is slightly less (5.4 +/- 0.8 kJ . mol-1) than the corresponding value for globular proteins.