Viscoelastic and light scattering studies on thermally induced sol to gel phase transition in fish myosin solutions

Viscoelastic (VE) and dynamic light scattering (DLS) analyses of fish (white croaker) myosin solutions were performed at myosin concentrations of 30 mg/mL for VE and 0.1 mg/mL for DLS at 0.6M KCl and pH 7.0 to clarify thermally induced gelation. The hydrodynamic radius R(h) considerably decreased around 30-35 degrees C. The shear modulus G was constant below 25 degrees C and increased by incubating the sample at 30 degrees C. G further increased as the temperature of the incubated sample decreased. The curves of G vs T for different time courses showed a sharp peak around 35 degrees C and a moderate peak around 60 degrees C in the heating process, while a stepwise increase in G was observed around 30 degrees C in the cooling process when the temperature was elevated to not more than 60 degrees C. No distinct stepwise change was observed once the temperature of the sample exceeded 60 degrees C. The absolute value of G strongly depended on the maximum elevated temperature and the incubation time at that temperature. The corresponding behavior of the viscosity eta was observed for each time course. Based on these results, the mechanism of thermally induced gelation of myosin solutions is discussed in view of S-S bridge formation in the head and tail portions and unwinding/rewinding of coiled-coil alpha-helices in the tail portion.