Myosin filament depolymerizes in a low ionic strength solution containing l-histidine

Myosin, one of the major myofibrillar proteins, forms a filamentous polymer and is insoluble in physiological and low ionic strength solutions. We have shown that myosin is soluble in a low ionic strength solution containing l-histidine. In this study, to clarify the role of l-histidine in the solubilization of myosin, we investigated effects of l-histidine on the filament formation and the morphology of myosin at a low ionic strength. In the presence of l-histidine, myosin formed a filamentous polymer in a physiological ionic strength solution and dispersed in a low ionic strength solution. Transmission electron microscopy showed that light meromyosin (LMM), the rod region of myosin, in a low ionic strength solution containing l-histidine was longer than that in a high ionic strength solution without l-histidine. l-histidine causes the elongation of LMM region of myosin contributing to the weakening of the myosin filament and the dissociation of myosin in a low ionic strength solution.