A myofibrillar component that modifies the actin-myosin interaction in postrigor skeletal muscle

A protein component that modified the interaction between actin and myosin was released from myofibrils on Ca2+-treatment, accompanying the weakening of Z disks. For its release 10(-4) M Ca2+ was required. The presence of the component facilitated the dissociation of thin and thick filaments from myofibrils and delayed superprecipitation of reconstituted actomyosin, independently of Ca2+ concentration. The component is probably a constituent of Z disks. In postmortem muscle, it is possible that the component is released from Z disks with an increased concentration of Ca2+, and that it weakens rigor linkages formed between actin and myosin, giving rise to lengthening of rigor-shortened sarcomeres.