Polymerization of myosin from smooth muscle of the calf aorta

Myosin from smooth muscle of the calf aorta has been found to be similar to rabbit skeletal muscle myosin in molecular weight, sedimentation coefficient, and amino acid composition. When dialyzed at low ionic strength, it also forms polymers that exist in equilibrium with the "monomer", the position of this equilibrium being sensitive to ionic strength, pH, and hydrostatic pressure. The self-association reactions for smooth muscle myosin differ, however, from those observed for skeletal muscle myosin in several ways: (1) aorta myosin polymerizes at a higher ionic strength to form a smaller polymer; (2) between pH 6 and 8, only one polymer boundary is observed; (3) the result of varying total protein concentration on the myosin-polymer equilibrium cannot be analyzed by the Gilbert theory for a simple two-species system, as was possible with skeletal myosin. This more complex polymerization behavior may be related to differences in the mode of assembly between smooth and skeletal muscle myosin.