Biophysical Journal 56: 517-523 (1989)
© 1989 the Biophysical Society

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Barnett, V A Articles by Thomas, D D Search for Related Content PubMed PubMed Citation Articles by Barnett, V A Articles by Thomas, D D

Microsecond rotational motion of spin-labeled myosin heads during isometric muscle contraction. Saturation transfer electron paramagnetic resonance.

Department of Biochemistry, University of Minnesota Medical School, Minneapolis 55455.

ABSTRACT

We have used saturation transfer electron paramagnetic resonance (ST-EPR) to detect the microsecond rotational motions of spin-labeled myosin heads in bundles of skinned muscle fibers, under conditions of rigor, relaxation, and isometric contraction. Experiments were performed on fiber bundles perfused continuously with an ATP-regenerating system. Conditions were identical to those we have used in previous studies of myosin head orientation, except that the fibers were perpendicular to the magnetic field, making the spectra primarily sensitive to rotational motion rather than to the orientational distribution. In rigor, the high intensity of the ST-EPR signal indicates the absence of microsecond rotational motion, showing that heads are all rigidly bound to actin. However, in both relaxation and contraction, considerable microsecond rotational motion is observed, implying that the previously reported orientational disorder under these conditions is dynamic, not static, on the microsecond time scale. The behavior in relaxation is essentially the same as that observed when myosin heads are detached from actin in the absence of ATP (Barnett and Thomas, 1984), corresponding to an effective rotational correlation time of approximately 10 microseconds. Slightly less mobility is observed during contraction. One possible interpretation is that in contraction all heads have the same mobility, corresponding to a correlation time of approximately 25 microseconds. Alternatively, more than one motional population may be present. For example, assuming that the spectrum in contraction is a linear combination of those in relaxation (mobile) and rigor (immobile), we obtained a good fit with a mole fraction of 78-88% of the heads in the mobile state.(ABSTRACT TRUNCATED AT 250 WORDS)

This article has been cited by other articles:

				M. G. Bell, R. E. Dale, U. A. van der Heide, and Y. E. Goldman Polarized Fluorescence Depletion Reports Orientation Distribution and Rotational Dynamics of Muscle Cross-Bridges Biophys. J., August 1, 2002; 83(2): 1050 - 1073. [Abstract] [Full Text] [PDF]

				D. A. Lowe, D. D. Thomas, and L. V. Thompson Force generation, but not myosin ATPase activity, declines with age in rat muscle fibers Am J Physiol Cell Physiol, July 1, 2002; 283(1): C187 - C192. [Abstract] [Full Text] [PDF]

				D. A. Lowe, J. T. Surek, D. D. Thomas, and L. V. Thompson Electron paramagnetic resonance reveals age-related myosin structural changes in rat skeletal muscle fibers Am J Physiol Cell Physiol, March 1, 2001; 280(3): C540 - C547. [Abstract] [Full Text] [PDF]

				J. E. Baker, I. Brust-Mascher, S. Ramachandran, L. E. W. LaConte, and D. D. Thomas A large and distinct rotation of the myosin light chain domain occurs upon muscle contraction PNAS, March 17, 1998; 95(6): 2944 - 2949. [Abstract] [Full Text] [PDF]