Myosin content and filament structure in smooth and striated muscle

Fibres from four different muscles (rabbit psoas, guinea pig taenia coli, Lethocerus flight and leg) were glycerol-extracted, homogenized and dissolved in a sodium dodecyl sulphate solution. The relative mass of the myosin heavy chain and actin polypeptides present in these extracts was measured by polyacrylamide gel electrophoresis. The ratio was found to be consistent for each muscle and to differ widely between muscles. The results were used to calculate the number of myosin molecules per subunit repeat along the thick filaments of the striated muscles and ribbon-like filaments, and so to test a theory of filament structure.