Heat-induced gelation of myosin filaments.

Various lengths of myosin filaments were prepared by changing the speed of lowering the ionic strength. Short filaments were formed by rapid dilution and the filament length became longer with decreasing the speed of lowering the ionic strength. The average length of myosin filaments ranged from 0.5 to 3.0 μm with varying the speed of dilution. Myosin filament suspensions were heated to form gels, and those gel strengths were evaluated as rigidity. The rigidity depended on the length of the filaments before heating. The longer the filaments, the higher the rigidities. The gels with higher rigidity had a fine strand-like network structure. In contrast, that showing lower rigidity had a coarse aggregated structure. When low protein concentrations of myosin filament suspensions were heated at 40°C, myosin filaments associated with increasing the incubation time. When heating was done at 60°C, aggregation of myosin filaments occurred in a short time. Electron microscopic observation suggests that the association and the following aggregation of myosin filaments per se cause formation of a whole network structure. Short myosin filaments began to aggregate randomly in an early stage of heating and they made clusters. But long filaments did not form a cluster; instead, some of them associated side-by-side to form bundles. These differences in the mode of aggregation among various lengths of myosin filaments seemed to be one of possible reasons for the different network structures observed in the gels.