The adenosinetriphosphatase activity of myofibrils isolated from skeletal muscle

Abstract

Schick and Hass (Science 109 487, 1949) showed that myofibrils may be isolated by treating muscle with trypsin at 0[degree]C and pH 7. The authors, using rabbit psoas muscle, found trypsin unsatisfactory and used collagenase. At 0[degree]C low concns. of trypsin degrade the myofibril and destroy the actomyosin-forming ability of extracted myosin, yet at the same time have little effect on the adeno-sinetriphosphatase (ATPase] activity. Myofibrils isolated by the collagenase method show detailed fine structure in the electron microscope, and in the presence of ATP shorten and retain considerable organization of structure. The ATPase activity of isolated myofibrils is activated by both Ca and Mg. In the absence of other cations the extent of activation at pH 6.9 and 8.6 by 0.001-0.002 [image] Mg is of the same order as that obtained with optimum Ca concns. Unlike extracted actomyosin, intact myofibrils have Mg activated ATPase activity in the presence of 0.1 [image] KCl. Destruction of the organization by dissolving the myofibrils in 1.0 [image] KC1 transforms the Mg activation effect in 0.1 [image] KC1 to one of inhibition. This change from activation to inhibition is frequently obtained on storing and also after incubation at 37[degree]C. Normal prepns. have myokinase activity which can be almost entirely removed by repeated washing at the centrifuge. It is concluded that actomyosin alone is responsible for both the Ca and Mg activated ATPase activity of the myofibrils isolated by the collagenase method.