1. Denaturation of purified myosin and its enzymically active subfragments, heavy meromyosin, subfragment 1 and subfragment 1-n have been studied under the various conditions.
2. Although the dependence on pH and temperature of denaturation of myosin subfragments has been shown to be almost the same as those of the parent protein, the rate of the reaction increases gradually until myosin molecules are fragmented to globular heads.
3. The dependence on ionic strength of the rates of denaturation particularly indicates that myosin is stabilized at higher ionic strength, suggesting that the rod region of myosin molecule plays some role for the stability of the protein in solution.
4. Aggregation which accompanies denaturation has been found in all denaturation reactions examined, and free sulfhydryl groups on and in the protein molecules have been confirmed to have nothing to do with this phenomenon.
5. No liberation of small subunit (g-subunit) from heavy meromyosin and subfragment 1 was detectable during the course of thermal denaturation.
6. The first-order rate constant determined from analyses of sedimentation velocity diagrams and gel-filtration profiles has coincided with that determined from loss of ATPase activities with time of incubation under the same conditions, only when the subfragment I was used as material.
7. While glucose and ATP act as inhibitors of denaturation reaction of myosin and its subfragments, a protective effect of 10 mM PPi has been depleted as myosin is fragmented into smaller subfragments.
8. The influence of this anion on the denaturation of myosin and the possible mechanism and intermolecular interactions among molecules in the denaturation process are discussed.