Biophysical Journal 71: 341-350 (1996)
© 1996 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 Diffee, G M Articles by Moss, R L Search for Related Content PubMed PubMed Citation Articles by Diffee, G M Articles by Moss, R L

Altered kinetics of contraction in skeletal muscle fibers containing a mutant myosin regulatory light chain with reduced divalent cation binding.

Department of Physiology, University of Wisconsin, Madison 53706, USA. gmdiffee@facstaff.wisc.edu

ABSTRACT

We examined the kinetic properties of rabbit skinned skeletal muscle fibers in which the endogenous myosin regulatory light chain (RLC) was partially replaced with a mutant RLC (D47A) containing a point mutation within the Ca2+/Mg2+ binding site that severely reduced its affinity for divalent cations. We found that when approximately 50% of the endogenous RLC was replaced by the mutant, maximum tension declined to approximately 60% of control and the rate constant of active tension redevelopment (ktr) after mechanical disruption of cross-bridges was reduced to approximately 70% of control. This reduction in ktr was not an indirect effect on kinetics due to a reduced number of strongly bound myosin heads, because when the strongly binding cross-bridge analog N-ethylmaleimide-modified myosin subfragment1 (NEM-S1) was added to the fibers, there was no effect upon maximum ktr. Fiber stiffness declined after D47A exchange in a manner indicative of a decrease in the number of strongly bound cross-bridges, suggesting that the force per cross-bridge was not significantly affected by the presence of D47A RLC. In contrast to the effects on ktr, the rate of tension relaxation in steadily activated fibers after flash photolysis of the Ca2+ chelator diazo-2 increased by nearly twofold after D47A exchange. We conclude that the incorporation of the nondivalent cation-binding mutant of myosin RLC decreases the proportion of cycling cross-bridges in a force-generating state by decreasing the rate of formation of force-generating bridges and increasing the rate of detachment. These results suggest that divalent cation binding to myosin RLC plays an important role in modulating the kinetics of cross-bridge attachment and detachment.

This article has been cited by other articles:

				K. Burton, R. M. Simmons, J. Sleep, R. M. Simmons, K. Burton, and D. A. Smith Kinetics of force recovery following length changes in active skinned single fibres from rabbit psoas muscle: with an Appendix: Analysis and modelling of the late recovery phase J. Physiol., June 1, 2006; 573(2): 305 - 328. [Abstract] [Full Text] [PDF]

				J. J. Sherwood, G. S. Waller, D. M. Warshaw, and S. Lowey A point mutation in the regulatory light chain reduces the step size of skeletal muscle myosin PNAS, July 27, 2004; 101(30): 10973 - 10978. [Abstract] [Full Text] [PDF]

				G. M. Diffee, E. A. Seversen, and M. M. Titus Exercise training increases the Ca2+ sensitivity of tension in rat cardiac myocytes J Appl Physiol, July 1, 2001; 91(1): 309 - 315. [Abstract] [Full Text] [PDF]

				S. J. Simnett, E. C. Johns, S. Lipscomb, I. P. Mulligan, and C. C. Ashley Effect of pH, phosphate, and ADP on relaxation of myocardium after photolysis of diazo 2 Am J Physiol Heart Circ Physiol, September 1, 1998; 275(3): H951 - H960. [Abstract] [Full Text] [PDF]

				D. M. Warshaw, W. H. Guilford, Y. Freyzon, E. Krementsova, K. A. Palmiter, M. J. Tyska, J. E. Baker, and K. M. Trybus The Light Chain Binding Domain of Expressed Smooth Muscle Heavy Meromyosin Acts as a Mechanical Lever J. Biol. Chem., November 17, 2000; 275(47): 37167 - 37172. [Abstract] [Full Text] [PDF]