A loss of actin from shell-fish myofibrils and fish myosin B during wash-treatment

When myofibrils were prepared from various muscles of shell-fish and of fish by repeated washing with low ionic strength medium, more actin was released from the shell-fish myofibrils than from the fish myofibrils. This conclusion was based on the following results. (1) The inactivation mode of Ca-ATPase activity changed from the typical first-order process to biphasic first-order behavior: the rate for inactivation increased as the washing repeated. (2) The typical first-order inactivation of Ca-ATPase was reversibly restored by the addition of rabbit skeletal F-actin to the washed myofibrils. (3) A component corresponding to actin on the SDS-gel electrophoresis was specifically decreased in the washed myofibrils, while it was increased in the supernatant and precipitated upon complexing the myosin.