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 0degreesC 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.