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We used light scattering and ultracentrifugation to study the binding ratio of myosin and actin from normal and failing dog hearts and to determine the effect of temperature and adenosine triphosphate (ATP) on the binding. For comparison, similar studies were done on myosin and actin from rabbit skeletal muscle. We found a higher combining ratio, by weight, for cardiac myosin and actin (4.8 : 1) than for skeletal myosin and actin (4.4 : 1). The dissociation constants were similar at 24°C for cardiac and skeletal proteins. But at 10°C, the dissociation constant was greater for cardiac proteins, and the difference appeared more pronounced when phosphate was used to buffer the solutions. The dissociation constant at 10°C was greater for myosin and actin from failing dog hearts. ATP caused dissociation of cardiac and skeletal F-acto-heavy meromyosin and F-actomyosin. There was evidence that the binding of cardiac proteins may not be as tight as that of skeletal muscle proteins.

For Archibald molecular weight calculations measurements are made along a single Rayleigh fringe. The displacement of the fringe measured as a function of the radial distance, x , is used to obtain the concentration gradient d c /d x by fitting a second-degree polynomial in x , extrapolating and differentiation. Good agreement with published values of the molecular weight was obtained with solutions of RNAase and of bovine serum albumin. Also described is a graphical method for obtaining d c /d x from a tangent to the fringe drawn upon a photographic enlargement.

Overlap integrals between 3dσ orbitals, between 5dσ orbitals, and between 3dσ and 5dσ orbitals have been computed using an IBM 650 MDDPM. The program is briefly discussed. Analytic relations between dσ—dσ coxial and symbactic overlap integrals are derived.

Three modified particle‐in‐a‐box models for the excited state of the charge‐transfer‐to‐solvent spectra of aqueous halide ions are derived. In two of these (I and II), the halogen atom is represented as a potential well within the box, and its effect on the energy is calculated by first‐order perturbation theory. In I, the excited state is the n = 1 level of the box, and in II, the n = 2 level. In the third model (III, the halide atom is represented as a hard sphere. In this extension of the previous model, the thickness of the spherical shell between the hard sphere and the box replaces the radius of the box as the factor that determines the energy of the excited electron. This model is energetically similar to the previous one, but differs from it in that the overlap between the wavefunctions of the ground and excited states can be adjusted by varying the radius of the hard sphere.

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.