Studies on heat-induced gelation of cardiac myosin and actomyosin. Part I. Effects of temperature, actin-myosin ratio, pH, and salt and protein concentrations on heat-induced gelling of cardiac myosin and reconstituted actomyosin.

Heat-induced gel forming ability of cardiac myosin and reconstituted actomyosin at different weight ratios was investigated in a model system. In this study, myosin alone always had greater binding power than actomyosin under identical conditions of temperature, pH, and salt and protein concentrations. Especially, myosin formed the strongest three-dimensional gel structure with fine filaments and uniform porosity at pH 5.4 and salt concentration <0.2M KCl on heating to 65°C. We also found that the "cross-linking" role of F-actomyosin, if any, does not seem necessary for enhancing the binding strength, at least of cardiac myosin, since the incorporation of actin in different proportion into the myosin system always produced a weaker gel than that formed by myosin alone at identical protein concentration and thermal processing conditions. However, among acto-myosin complexes, the one with 1:15 weight ratio always yielded a stronger gel than that formed by actomyosin with other ratios of pH 6.0 and 0.6 M KCl. The gel-forming potential of isolated myosin declined with prolonged storage at 4°C. In view of the similarity of the thermogel behavior of cardiac myosin to that of skeletal myosin filaments formed at low salt concentrations, the relationship between the high gelation ability and the native polymer (filament) formability of cardiac myosin is discussed.