Hydrostatic Pressure-induced Aggregation of Myosin Molecules in 0.5M KCl at pH 6.0

Myosin dissolved in 0.5M KCl at pH 6.0 was exposed to hydrostatic pressure up to 210MPa for 30min. Turbidity of myosin solutions did not change after application of pressure at 70MPa, while it gradually increased with extending duration of pressurization at 140MPa, and it markedly increased within 5min at 210MPa. Sedimentation velocity measurements indicated that myosin molecules associated to form aggregates upon pressurization. Electron microscopic observation confirmed that increasing hydrostatic pressure induced aggregation of myosin molecules. After exposure to and release of 70MPa, most myosin molecules were in the monomeric state like the unpressurized control ; however, some monomeric myosin had a one-headed shape instead of the two heads of an intact molecule. With increasing pressure, myosin heads were tightly packed, forming a clump and the tails of myosin molecules extended radially from the clump. Neither tail to head nor tail to tail interaction occurred. The shape of pressure-induced oligomer looked like a daisy-wheel and its morphology was similar to that of heat-induced oligomer reported previously (Yamamoto et al., 1990). Myosin solution did not form a gel by pressurization alone, though pressure-treated myosin formed a gel upon following heating. Pressurization up to 210MPa did not affect the gel strength or the microstructure of heat-induced gel.