Backbone and side-chain motion in myosin, subfragment 1, and rod determined by natural abundance carbon-13 NMR.

We report natural abundance carbon-13 nuclear magnetic resonance studies of myosin, subfragment 1 (S-1), and myosin rod in solution and of myosin filaments. We measured solution spectra at 37.7 MHz, 20 degrees C with scalar proton decoupling. If the native proteins were rigid particles, only S-1 would have observable intensity. In fact, 30% of myosin, 70% of S-1, and 30% of rod carbons are observable. Observable carbons possess rotational correlation times less than 10(-7) s which effectively average 13C-1H dipolar coupling and anisotropic chemical shift interactions. Short alpha-carbon region spin-lattice relaxation times (T1) and nonminimal 13C-1H nuclear Overhauser enhancements suggest restricted nanosecond motions of backbone atoms. This is direct evidence for internal motion of backbone and side-chain carbons in myosin and its fragments. Double resonance experiments at 15.1 MHz and 5 degrees C with pelleted myosin filaments detected carbon atoms in rigid domains. While most (80%) aliphatic carbons are strongly 13C-1H dipolar coupled due to limited motion, they have short T1 values and large nuclear Overhauser enhancement values; this is evidence for high frequency restricted motion. Cross-polarization experiments show that the 13C carbonyl line width is motionally narrowed, suggesting broad backbone motions in the 100 mus range. Thus, motion in filaments is highly anisotropic.

Force-length relations of glycerinated rabbit psoas.

Force-length curves of glycerinated rabbit psoas were determined in media of physiological interest. In one set of experiments the free [Ca++] was constant at 10(-5) M and the [MgATP] varied. At low [MgATP] the elastic properties are those of a highly ordered, inextensible fiber; at high [MgATP] they are representative of a much more elastic body. At intermediate concentrations sigmoidal shaped curves were observed as were also found when [MgATP] was constant and the free [Ca++] varied. These curves closely resemble coexistence curves that have been reported for fibrous proteins.

The observation of cis residues in poly(L-proline) in aqueous solution.

Proton Fourier transform NMR spectra at 270 MHz were obtained for three different molecular weight samples of poly(L-proline) in D2O. A weak, but clearly discernable, resonance at 4.3 ppm was observed in each case with an integrated intensity about 2-3% of the Calpha trans proton resonance. Based on the Torchia-Bovey assignment this resonance is attributed to the Calpha cis proton. The presence of cis residues, even in this small concentration, necessitates a reexamination of the conformational properties of this polymer. Definite conclusions cannot be reached from spectra obtained in organic solvents because of the much smaller separation between the cis and trans resonances.

Glycerinated muscle fibers: relation between isometric tension and adenosine triphosphate hydrolysis.

The isometric tension of glycerinated muscle fibers and the adenosine triphosphatase activity of homogenates were determined as a function of the concentration of adenosine triphosphate without the addition of divalent cations. These two phenomena are not parallel; large tensions can be developed with negligible hydrolysis of adenosine triphosphate. It is concluded that the large negative free energy change of the hydrolysis is not required for shortening or development of tension.

Some fundamental molecular mechanisms of contractility in fibrous macromolecules.

The fundamental molecular mechanisms of contractility and tension development in fibrous macromolecules are developed from the point of view of the principles of polymer physical chemistry. The problem is treated in a general manner to encompass the behavior of all macromolecular systems irrespective of their detailed chemical structure and particular function, if any. Primary attention is given to the contractile process which accompanies the crystal-liquid transition in axially oriented macromolecular systems. The theoretical nature of the process is discussed, and many experimental examples are given from the literature which demonstrate the expected behavior. Experimental attention is focused on the contraction of fibrous proteins, and the same underlying molecular mechanism is shown to be operative for a variety of different systems.