Thermal denaturation and aggregation of chicken breast muscle myosin and subfragments

To elucidate the roles of the head and tail portions of chicken breast muscle myosin in gelation, the thermal stability and aggregation behavior of myosin and seven subfragments in 0.6 M NaCl, pH 6.5, were investigated, namely, myosin heavy chain (MHC), light chains (LC), heavy meromyosin (HMM), light meromyosin (LMM), rod, subfragment 2 (S-2), and subfragment 1 (S-1). Myosin had four independent cooperative endothermic transitions (T_m) at 47, 54, 57, and 63 °C and aggregated from 50 to 70 °C. The MHC endotherm had peaks at 46, 54, and 64 °C and aggregated between 45 and 63 °C. S-1 unfolded in a single transition, having a T_m of 47.7 °C, and aggregated from 49 to 53 °C. The rod melted between 30 and 63.3 °C and continuously aggregated over this temperature range. Initial unfolding of the rod occurred in the LMM region. S-2 was primarily responsible for denaturation and aggregation above 55 °C. Transition temperatures of 48 and 57 °C were recorded for LC; however, no aggregation occurred. The rod had the biggest influence on gel formation. Light meromyosin and S-1 contributed to gel structure at temperatures less than about 55 °C, whereas S-2 was responsible for matrix formation above 60 °C.