Atomic Force Microscopic Investigation of Heat- or Pressure-Denatured Myosins and its Subfragments

Abstract

Myosin molecules are associated into filament at physiological condition such as 0.1 M NaCl. Since myosin filaments form a gel by application of hydrostatic pressure above 200 MPa without heating, the possibility of the meat processing by the pressure treatment is suggested. Both of heat- or pressure-induced filamentous myosin gels showed similar internal structure; namely, the gels were composed of a fine-strand network, whereas the elasticities of those two gels were different. The aim of this study is to clarify the relation between morphological and rheological properties of filamentous myosin gels using atomic force microscope (AFM). The heat- or pressure-treated myosin filament was investigated by AFM in 0.1 M NaCl without chemical fixation. The thermal- and pressure-induced strands, which were formed from denatured filaments, became knobby with elevating temperature and pressure. The strands were formed by side-by-side association of several filaments above 55 °C and 300 MPa. There was also no significant morphological difference between thermal and pressure-induced strands. The elasticities of strands were also investigated using an AFM. The elasticity of heat-induced strand showed maximal value (10.24±1.16 MPa) at 55 °C. On the other hand, the elasticity of pressure-induced strand increased with elevating pressure, and the maximal value was 9.80±0.84 MPa at 500 MPa. The elasticity of the whole gel corresponded with those of the strand. Myosin molecule consists of two globular heads (S1) attached to a tail (rod). The structure and elasticities of heat- and pressure-denatured subfragments were investigated using AFM. The heat- and pressure-denatured S1 showed similar aggregated structure, and the elasticities of denatured S1 aggregates increased with elevating application of temperature and pressure. On the other hands, the elasticity of heat-denatured rod filament showed maximal value at 55 °C, while that of pressure-denatured rod filament increased with elevating pressure. From these results, we conclude that the rheological characteristics of heat-denatured rod filaments determine the elasticity of heat-induced filamentous myosin gel, whereas that of pressure-denatured head and tail affects the rheological properties of pressure-induced myosin filament gel.