Structural studies of natural actomyosin from thermally acclimated frogs.

Natural actomyosin was isolated from skeletal muscle of frogs (Rana catesbeiana) acclimated at 25 degrees C and 5 degrees C. It was found that preparations isolated from warm-acclimated frogs may display considerable degradation of myosin heavy chains as compared with preparations isolated from cold-acclimated frogs. However, degradation may be minimized by inclusion of protease inhibitors during purification, indicating enhanced protease activity in preparations of natural actomyosin from warm-acclimated frogs. When purified in the presence of protease inhibitors, natural actomyosin from both warm-acclimated and cold-acclimated frogs exhibits comparable subunit composition of SDS-gel electrophoresis. The overall gel pattern is similar to that obtained from rabbit natural actomyosin except that in the frog, troponin-T and troponin-C appear to co-migrate with tropomyosin and myosin light chain 2, respectively.