Protein, a New Fibrous Protein of Skeletal Muscle: Complex Formation With Myosin

¹ From the Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland, and the Marine Biological Laboratory, Woods Hole, Massachusetts

A complex, -myosin, is formed by the union of myosin with protein. This complex may be demonstrated in several ways: a) it appears as a separate peak on the patterns of descending boundaries in electrophoresis, and has a mobility intermediate between the mobilities of myosin and D protein. b) It may be detected in the patterns of the ascending boundaries by the increase in the area of the myosin peak and the decrease in the area of free D protein. c) It may be seen in ultracentrifuge diagrams, and is best demonstrated in the synthetic boundary cell. In the mixtures of the three fibrous proteins, myosin, actin and protein, it can be shown that -myosin exists in the presence of an excess of actin. When isoviscous solutions of protein and actomyosin are mixed, there is a rapid fall in viscosity. This fall indicates that some of the actomyosin has been dissociated. The protein then unites with the free myosin to form -myosin. Since -myosin sediments more slowly than does the free myosin, and since the viscosity falls slightly when isoviscous solutions of protein and myosin are mixed, we suggest that the myosin molecule is split during formation of the complex.