[Interaction of alpha-actinin and tropomyosin with F-actin]

The interaction of alpha-actinin, F-actin and tropomyosin has been investigated by using electron microscopy, SDS-gel electrophoresis and viscosimetry. It was shown that the temperature dependence of the interaction with F-actin was similar for alpha-actinins, isolated from the muscle of warmblooded animal (rabbit skeletal muscle) and from muscle of cold--blooded ones (cross striated part of the adductor of scallop Patinopecten yessoensis). The temperature rise from 0 degrees C to 37 degrees C results in a decrease of the affinity of alpha-actinin to F-actin. Tropomyosin decreases the amount of alpha-actinin bound to F-actin at 37 degrees C, but does not dislodge it completely from F-actin filaments. In this case the alpha-actinin binding also occurs along the entire length of the F-actin. It has also been shown that at 0 degrees C alpha-actinin and tropomyosin interact with F-actin independently of each other. The data obtained attest that tropomyosin and alpha-actinin have different binding sites on F-actin. The temperature and tropomyosin regulate only the amount of the bound alpha-actinin, but not its localization on the actin filament, as it was earlier supposed. These data allow one to conclude that the localization of alpha-actinin in Z-disk of cross-striated muscle can be determined neither by physiological temperature nor the presence of tropomyosin.