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

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Abstract
A complex, Δ-myosin, is formed by the union of myosin with Δ 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 Δ protein, it can be shown that Δ-myosin exists in the presence of an excess of actin. When isoviscous solutions of Δ protein and actomyosin are mixed, there is a rapid fall in viscosity. This fall indicates that some of the actomyosin has been dissociated. The Δ protein then unites with the free myosin to form Δ-myosin. Since Δ-myosin sediments more slowly than does the free myosin, and since the viscosity falls slightly when isoviscous solutions of Δ protein and myosin are mixed, we suggest that the myosin molecule is split during formation of the complex.

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