Comparative analyses of the kinetics and subunits of myosins from canine skeletal muscle and cardiac tissue.

Two types of canine cardiac myosins, myosin from the free wall of the right ventricle and the free wall of the left ventricle, were compared with canine skeletal muscle myosin from the gastrocnemius. The Vmax values for the ATPase reaction catalyzed by myosin were significantly different among the three types of tissues. For K+-activated myosin the Vmax values in micromoles of Pi per mg per min were: right ventricle, 0.57; left ventricle, 0.72; and gastrocnemius, 0.95. For Ca-2+ -activated myosin the Vmax values were: right ventricle, 0.32; left ventricle, 0.42; gastrocnemius, 0.50. All differences were significant (p smaller than 0.001). For all three types of tissues the Vmax values for NH4+ -activated myosin were the same (2.30). Light chains among all three types of tissues were immunologically identical, whereas the heavy chains of the two cardiac ventricles were immunologically identical with each other; however both were immunologically nonidentical with those of the gastrocnemius. The proportion of myosin light chains to heavy chains was different in the three types of tissue. Of the total protein present in each of the myosins, there was 18% in the light chains of right ventricle myosin, 10% in the light chains of left ventricle myosin, and 13% in the light chains of gastrocnemius. Both left ventricle myosin and myosin from gastrocnemius had significantly less C1d light chain, as compared to myosin from the right ventricle.