AN ELECTRON MICROSCOPE STUDY OF CANINE CARDIAC MYOSIN AND SOME OF ITS AGGREGATES

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Abstract
The morphology of the canine cardiac myosin molecule has been investigated in the electron microscope with Hall''s mica-replica technique. The molecule is an elongated rod (shaft) of nonuniform diameter with globular expansion (head) on one end. Statistical analysis of the lengths of 1908 molecules showed that the mean length was 1610 [plus or minus] 250 A; the mean length of the head was 210 + 20 A; and the diameter of the head and that of the shaft were 35 to 40 and 15 to 20 A, respectively. About one-third of the molecules had single or multiple, fairly sharp, angulations along their shafts. Rarely, some details of the substructure of the molecule have been observed. Large, spindle-shaped aggregates, measuring 0.5 to 1 [mu] in length and 50 to 100 A in diameter, were produced by dilution of the myosin solutions. These aggregates were readily visualized in the electron microscope by means of Huxley''s negative-staining technique. Projections often were visible along the length of the aggregates except at a central zone where they were frequently absent. The aggregates resembled the thick myofilaments of the myocardium and appeared similar to those produced by Huxley from skeletal myosin solutions.