Biophysical Journal 73: 2292-2303 (1997)
© 1997 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 Xu, S Articles by Yu, L C Search for Related Content PubMed PubMed Citation Articles by Xu, S Articles by Yu, L C

X-ray diffraction studies of cross-bridges weakly bound to actin in relaxed skinned fibers of rabbit psoas muscle.

National Institutes of Health, Bethesda, Maryland 20892, USA.

ABSTRACT

X-ray diffraction patterns were obtained from skinned rabbit psoas muscle under relaxing and rigor conditions over a wide range of ionic strengths (50-170 mM) and temperatures (1 degree C-30 degrees C). For the first time, an intensification of the first actin-based layer line is observed in the relaxed muscle. The intensification, which increases with decreasing ionic strength at various temperatures, including 30 degrees C, parallels the formation of weakly attached cross-bridges in the relaxed muscle. However, the overall intensities of the actin-based layer lines are low. Furthermore, the level of diffuse scattering, presumably a measure of disorder among the cross-bridges, is little affected by changing ionic strength at a given temperature. The results suggest that the intensification of the first actin layer line is most likely due to the cross-bridges weakly bound to actin, and that the orientations of the weakly attached cross-bridges are hardly distinguishable from the detached cross-bridges. This suggests that the orientations of the weakly attached cross-bridges are not precisely defined with respect to the actin helix, i.e., nonstereospecific. Intensities of the myosin-based layer lines are only marginally affected by changing ionic strength, but markedly by temperature. The results could be explained if in a relaxed muscle the cross-bridges are distributed between a helically ordered and a disordered population with respect to myosin filament structure. Within the disordered population, some are weakly attached to actin and others are detached. The fraction of cross-bridges in the helically ordered assembly is primarily a function of temperature, while the distribution between the weakly attached and the detached within the disordered population is mainly affected by ionic strength. Some other notable features in the diffraction patterns include a approximately 1% decrease in the pitch of the myosin helix as the temperature is raised from 4 degrees C to 20 degrees C.

This article has been cited by other articles:

				S. Xu, D. Martyn, J. Zaman, and L. C. Yu X-ray Diffraction Studies of the Thick Filament in Permeabilized Myocardium from Rabbit Biophys. J., November 15, 2006; 91(10): 3768 - 3775. [Abstract] [Full Text] [PDF]

				S. Xu, J. Gu, B. Belknap, H. White, and L. C. Yu Structural Characterization of the Binding of Myosin{middle dot}ADP{middle dot}Pi to Actin in Permeabilized Rabbit Psoas Muscle Biophys. J., November 1, 2006; 91(9): 3370 - 3382. [Abstract] [Full Text] [PDF]

				A. S. Brack, B. D. Brandmeier, R. E. Ferguson, S. Criddle, R. E. Dale, and M. Irving Bifunctional Rhodamine Probes of Myosin Regulatory Light Chain Orientation in Relaxed Skeletal Muscle Fibers Biophys. J., April 1, 2004; 86(4): 2329 - 2341. [Abstract] [Full Text] [PDF]

				D. A. Martyn, B. B. Adhikari, M. Regnier, J. Gu, S. Xu, and L. C. Yu Response of Equatorial X-Ray Reflections and Stiffness to Altered Sarcomere Length and Myofilament Lattice Spacing in Relaxed Skinned Cardiac Muscle Biophys. J., February 1, 2004; 86(2): 1002 - 1011. [Abstract] [Full Text] [PDF]

				N. A. Koubassova and A. K. Tsaturyan Direct Modeling of X-Ray Diffraction Pattern from Skeletal Muscle in Rigor Biophys. J., August 1, 2002; 83(2): 1082 - 1097. [Abstract] [Full Text] [PDF]

				N. Fukuda, D. Sasaki, S.'i. Ishiwata, and S. Kurihara Length Dependence of Tension Generation in Rat Skinned Cardiac Muscle: Role of Titin in the Frank-Starling Mechanism of the Heart Circulation, October 2, 2001; 104(14): 1639 - 1645. [Abstract] [Full Text] [PDF]

				R. J. Solaro and H. M. Rarick Troponin and Tropomyosin : Proteins That Switch on and Tune in the Activity of Cardiac Myofilaments Circ. Res., September 7, 1998; 83(5): 471 - 480. [Abstract] [Full Text] [PDF]