Characterization of Myosin from Normal Dog Heart

Cardiac myosin and congestive heart failure in the dog

Chronic congestive heart failure has been produced in dogs by surgical induction of valvular disease. Cardiac myosin was isolated from the normal dogs and from dogs with congestive heart failure and characterized. Physicochemical properties of the cardiac myosins were determined by measurements of velocity sedimentation, partial specific volume, rate of diffusion, limiting viscosity number, light-scattering behavior, and ATPase activity. The measurements show that normal cardiac myosin (myosin C) has a molecular weight of 225,000, whereas myosin from the failing heart (myosin F) has a molecular weight of 690,000. This change in molecular weight occurs without a marked alteration in amino acid composition and suggests that end-to-end trimerization of normal cardiac myosin occurs in association with congestive heart failure in the dog. There was no significant change in ATPase activity.

Hydrodynamic studies on the self association of vertebrate skeletal muscle myosin

Sedimentation velocity studies on myosin A solutions at high ionic strength combined with computer-simulation of the concentration dependence of the sedimentation coefficient for a rapidly reversible monomer-dimer equilibrium have confirmed that if such an equilibrium does exist it has an equilibrium constant of less than 10 ml/g. A new hydrodynamic treatment has been used to calculate the molecular weight of myosin from s0 and ks alone and has yielded a value of 470 000. Combination of viscosity and sedimentation velocity results has shown that the myosin molecule displays little swelling (Vs/v = 1.1 +/- 0.1). A new picture of the myosin molecule is presented in which a conformational change in the head region is suggested to account for the variation in published s 0 values.

Heart contractile proteins

That several proteins of the sarcomere differ from one muscle to the next is well documented, and it is becoming evident that homogeneous muscles, like the heart, are also species specific. 1) Clear-cut evidence is available concerning myosin, and, to date, several types of molecules have been described. a) The myosins of white skeletal, heart, and smooth muscle differ in the activity of their Ca2+ and K+ATPases, as also in the structure of their light subunits. b) The Ca2+ATPases of the various cardiac myosins have been shown to exhibit species differences and correlate with the speed of shortening of the muscle. 2) The structures of tropomyosin, some troponin components, and alpha actinin (but not actin) appear to be unlike in the different types of muscle. 3) These phylogenic modifications may be related to the changes characteristic of the particular muscles under pathological conditions, which are accompanied by substantial increase in protein synthesis.

Cardiac myosin adenosinetriphosphatase of rat and mouse. Distinctive enzymatic properties compared with rabbit and dog cardiac myosin

Cardiac myosin obtained from rats and mice (smaller animals) had a higher adenosinetriphosphatase (ATPase) activity in the presence of calcium ions (Ca 2+ ) than did cardiac myosin from rabbits and dogs (larger animals). Structural differences between the two types of cardiac myosin were suggested by the lower apparent activation energy of the Ca 2+ activated ATPase reaction catalyzed by cardiac myosin from the smaller animals and by the lower rate of inactivation of ATPase at pH 9.0. No evidence for activators of myosin ATPase was found in heart muscle or cardiac myosin from rats and mice. The cardiac myosin from these animals was also distinctive with respect to the pattern of activation and inhibition of ATPase by salts and sulfhydryl reagents. ATPase activity of cardiac myosin from the smaller animals was less sensitive to the inhibitory effect of KCl in the presence of Ca 2+ and was not activated by N -ethylmaleimide, suggesting a difference in the myosin molecule at or near the active site. When sodium dodecyl sulfate-polyacrylamide gel electrophoresis was performed, no difference was observed in the molecular weight or the proportion of the light chains between the two types of cardiac myosin. ATPase activity of skeletal myosin was approximately the same in all animals and showed a pattern similar to that of the cardiac myosins from rabbits and dogs. The structural difference in the cardiac myosin from rats and mice suggested by these experiments appears to account for the enhanced myocardial contractility found in these animals.

Adenosinetriphosphatase activity of cardiac myosin. Comparison of the enzymatic activities and activation by actin of dog cardiac, rabbit cardiac, rabbit white skeletal and rabbit red skeletal muscle myosins

Examination of the ATPase activities of rabbit cardiac, rabbit red skeletal and rabbit white skeletal muscle myosins has demonstrated the existence of two types of myosin. One type, characterized by the higher ATPase activity, is present in white skeletal muscle; the other is found in red skeletal and cardiac muscle. The differences between myosin preparations could not be attributed to varying degrees of actin contamination nor to changes occurring in the myosins during the preparative procedure. Chromatography of dog cardiac myosin on DEAE-cellulose showed a single component. No differences were observed between the cardiac myosins of the dog and rabbit.

Activation of the ATPase activity of cardiac myosin by Ca ++ was less than that of white skeletal myosin while the extent of inhibition by Mg ++ was similar for both. The stoichiometry of the interaction with actin of both cardiac and white skeletal myosins was similar but actin caused less activation of the cardiac myosin ATPase. Cardiac and white skeletal actins showed no differences in their abilities to activate myosin ATPase activity, which is in accord with previously documented similarities in the structures of these actins.

Comparison of the present findings with previously reported mechanical measurements made with intact muscles does not indicate that the intrinsic level of myosin ATPase activity determines the maximal tension developed during the active state. On the other hand, there may be a direct relationship between shortening velocity and myosin ATPase activity.

Molecular Characteristics of Canine Cardiac Myosin

Cardiac myosin was obtained from the hearts of normal dogs by conventional extraction and precipitation techniques, followed by ammonium sulfate fractionation in the presence of 2.0 M lithium chloride. The molecular characteristics of this protein preparation are presented. Cardiac myosin prepared by this technique shows less tendency than conventionally prepared solutions to denature when stored at 0 to 4°C, and has a significantly higher ATP ase activity. Comparison of canine cardiac myosin and skeletal muscle myosin, obtained under identical conditions, revealed no differences between these two proteins in their intrinsic viscosities, S 20. w , molecular weight, and UV absorbances, although ATP ase activity was lower for cardiac myosin.

Comparison of Tropomyosins from Cardiac and Skeletal Muscle

No differences were found between the sedimentation coefficients, intrinsic viscosities, amino acid contents, and peptide patterns resulting from tryptic digestion of rabbit cardiac and skeletal tropomyosins. From sedimentation and viscosity data, the molecular weights of cardiac and skeletal tropomyosins were estimated to be 54,800 for both. This value is similar to previous estimates of the molecular weight of rabbit skeletal tropomyosin.

No evidence was obtained for the existence in heart muscle of tropomyosin A . Of the three more abundant contractile proteins of the heart, myosin, actin, and tropomyosin, only myosin appears to differ from its skeletal counterpart.