Chemical cross-linking of actin and myosin subfragment-1 in rigor complex

Chemical cross-linking of actin and myosin subfragment-1 (S-1) was investigated under various conditions. Actin and S-1 were cross-linked with the aid of zero-angstrom cross-linker 1-ethyl-3-(3-(dimethylamino)propyl) carbodiimide (EDC). Three new bands having larger molecular weight than those of two subunits of S-1 and one new, band having smaller molecular weight than the sub-units of S-1 appeared on electrophoretograms after the cross-linking reaction. These new bands were formed by cross-linking between actin and subcomponents of S-1. The extent of cross-linking decreased with increasing the ionic strength of reaction mixtures and also decreased with increasing the concentration of ATP. The extent of cross-linking between S-1 and actin prepared from fresh muscle was not appreciably smaller than that of those proteins prepared from postmortem muscle in rigor (stored at 0°C for 24 hr) and even that of those proteins prepared from muscle stored for more prolonged period (168 hr). To elucidate the effect of paratropomyosin on actin-S-1 interaction, the extent of actin-S-1 complex formation in the absence or presence of paratropomyosin during the cross-linking reaction was investigated. As a result, the formation of new bands was reduced after the addition of paratropomyosin, while almost no change of the intensity of S-1 heavy chain (90 kDa) was observed. The result indicates that paratropomyosin is involved in the weakening of actin-myosin interaction during the development of the resolution of rigor.