Effect on cardiac myosin of diverse methods of preparation

1. 1. Myosin was extracted from dog hearts and isolated by three methods which utilize ammonium sulfate fractionation and by two modifications of SZENT-GYORGYI'S dilution-precipitation method. 2. 2. The molecular weight of the myosin was determined by the YPHANTIS meniscus-depletion equilibrium method. 3. 3. Velocity sedimentation of the myosin using schlieren optics never revealed aggregation. Calculation of the molecular weight by the YPHANTIS method, however, revealed that several myosin samples were disperse. There is some evidence that dispersity may be avoided by using a method which includes a final high speed centrifugation. 4. 4. A statistically significant difference (P < 0.025) was demonstrated between the mean molecular weight, 4.76·105, of myosin prepared by MUELLER'S modification of SZENT-GYORGYI'S method and the mean molecular weight, 5.37·105, of the myosin prepared by all the methods which utilized ammonium sulfate fractionation. 5. 5. The best estimate of the molecular weight of myosin is 4.76·105. 6. 6. The calcium-activated ATPase activity was unaffected by the method of preparation.