Electron microscopy of myosin molecules from muscle and non-muscle sources

Myosin molecules from adult and embryonic vertebrate skeletal muscle, vertebrate cardiac muscle, vertebrate smooth muscle, invertebrate muscle, blood platelets and brain have been examined by a modification of Hall's mica-replication technique in which droplets of myosin in ammonium formate and glycerol solution are sprayed on a mica substrate at low temperature and then dried in vacuum prior to uni-directional shadowing with platinum. Myosin molecules from all these sources are morphologically indistinguishable and have two globular heads joined to a tail whose length does not differ by more than 10 nm from species to species. The absolute value of the tail length is 150 $\pm $ 20 nm (a larger error is given because of the difficulty in defining the point where the tail divides to give the two heads).