Characterizations of Cross-Bridges in the Presence of Saturating Concentrations of MgAMP-PNP in Rabbit Permeabilized Psoas Muscle

Frisbie, Suzanne M.; Xu, Sengen; Chalovich, Joseph M.; Yu, Linda Chia‐Hui

doi:10.1016/s0006-3495(98)78014-2

Cited by 13 publications

(13 citation statements)

References 48 publications

(54 reference statements)

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“…At the low concentrations of AMP-PNP used, the af®nity of S1 for actin was much higher than that of the S1±ATP complex. Note that at high concentrations of AMP-PNP, S1 does act like an S1±ATP complex in terms of actin binding (Frisbie et al 1998). Plots of the fraction of saturation of actin with S1 vs. the fraction of saturation with caldesmon could not be well ®tted by a simple model of competitive inhibition in either the presence or absence of tropomyosin.…”

Section: S T E P S I N T H E a T P As E C Y Cl E Af F E Ct -E D B Y Cmentioning

confidence: 99%

Caldesmon: binding to actin and myosin and effects on elementary steps in the ATPase cycle

Chalovich

Şen

Resetar

et al. 1998

Acta Physiologica Scandinavica

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The actin binding protein caldesmon inhibits the actin-activation of myosin ATPase activity. The steps in the cycle of ATP hydrolysis that caldesmon could inhibit include: (1) the binding of myosin to actin, (2) the transition between any two actin-myosin states and (3) the distribution between inactive and active states of actin. The analysis of these possibilities is complicated because caldesmon binds to both myosin and actin and because each caldesmon molecule binds to several actin monomers. This paper reviews procedures for analysing these interactions and summarizes current information on the stability and dynamics of the interaction of caldesmon with actin and myosin. Possible effects of caldesmon on transitions within the ATPase cycle of actomyosin are also discussed.

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Section: S T E P S I N T H E a T P As E C Y Cl E Af F E Ct -E D B Y Cmentioning

confidence: 99%

Caldesmon: binding to actin and myosin and effects on elementary steps in the ATPase cycle

Chalovich

Şen

Resetar

et al. 1998

Acta Physiologica Scandinavica

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“…Agents that increase the population or prolong the lifetime of one cross-bridge state over another potentially can provide access to intermediates that normally occur only as a small fraction of the myosin heads. 2,3-Butanedione monoxime and a number of ATP and P i analogues have been exploited extensively with this objective [3][4][5][6][7][8][9][10][11][12][13]. Lowering the temperature has also provided valuable information, since the kinetics of some of the steps are affected more than others [14,15].…”

Section: Introductionmentioning

confidence: 99%

Dimethyl sulphoxide enhances the effects of Pi in myofibrils and inhibits the activity of rabbit skeletal muscle contractile proteins

Mariano

Alexandre

SILVA

et al. 2001

Biochemical Journal

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In the catalytic cycle of skeletal muscle, myosin alternates between strongly and weakly bound cross-bridges, with the latter contributing little to sustained tension. Here we describe the action of DMSO, an organic solvent that appears to increase the population of weakly bound cross-bridges that accumulate after the binding of ATP, but before P i release. DMSO (5-30 %, v\v) reversibly inhibits tension and ATP hydrolysis in vertebrate skeletal muscle myofibrils, and decreases the speed of unregulated F-actin in an in itro motility assay with heavy meromyosin. In solution, controls for enzyme activity and intrinsic tryptophan fluorescence of myosin subfragment 1 (S1) in the presence of different cations indicate that structural changes attributable to DMSO are small and reversible, and do not involve unfolding. Since DMSO depresses S1 and acto-S1 MgATPase activities in

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“…Equilibrium is shifted toward the attached state by lowering the ionic strength (Brenner et al, 1982(Brenner et al, , 1984McKenna et al, 1989). Based on an effective actin concentration of 1 mM Frisbie et al, 1998) and a binding constant of S1 for actin in the presence of MgATP of ϳ7 ϫ 10 3 M Ϫ1 at 20 mM ionic strength (Chalovich et al, 1983;Frisbie et al, 1998), one may estimate that at ϭ 27 mM the fraction of crossbridges attached to actin could be as high as 80%, while at ϭ 170 mM the fraction is reduced to ϳ30%. Fig.…”

Section: Resultsmentioning

confidence: 99%

Structural Characterization of Weakly Attached Cross-Bridges in the A·M·ATP State in Permeabilized Rabbit Psoas Muscle

Melvin

et al. 2002

Biophysical Journal

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It is well established that in a skeletal muscle under relaxing conditions, cross-bridges exist in a mixture of four weak binding states in equilibrium (A*M*ATP, A*M*ADP*P(i), M*ATP, and M*ADP*P(i)). It has been shown that these four weak binding states are in the pathway to force generation. In the past their structural, biochemical, and mechanical properties have been characterized as a group. However, it was shown that the myosin heads in the M*ATP state exhibited a disordered distribution along the thick filament, while in the M*ADP*P(i) state they were well ordered. It follows that the structures of the weakly attached states of A*M*ATP and A*M*ADP*P(i) could well be different. Individual structures of the two attached states could not be assigned because protocol for isolating the two states has not been available until recently. In the present study, muscle fibers are reacted with N-phenylmaleimide such that ATP hydrolysis is inhibited, i.e., the cross-bridge population under relaxing conditions is distributed only between the two states of M*ATP and A*M*ATP. Two-dimensional x-ray diffraction was applied to determine the structural characteristics of the attached A*M*ATP state. Because the detached state of M*ATP is disordered and does not contribute to layer line intensities, changes as a result of increasing attachment in the A*M*ATP state are attributable to that state alone. The equilibrium toward the attached state was achieved by lowering the ionic strength. The results show that upon attachment, both the myosin and the first actin associated layer lines increased intensities, while the sixth actin layer line was not significantly affected. However, the intensities remain weak despite substantial attachment. The results, together with modeling (see J. Gu, S. Xu and L. C. Yu, 2002, Biophys. J. 82:2123-2133), suggest that there is a wide range of orientation of the attached A*M*ATP cross-bridges while the myosin heads maintain some degree of helical distribution on the thick filament, suggesting a high degree of flexibility in the actomyosin complex. Furthermore, the lack of sensitivity of the sixth actin layer line suggests that the binding site on actin differs from the putative site for rigor binding. The significance of the flexibility in the A*M*ATP complex in the process of force generation is discussed.

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Characterizations of Cross-Bridges in the Presence of Saturating Concentrations of MgAMP-PNP in Rabbit Permeabilized Psoas Muscle

Cited by 13 publications

References 48 publications

Caldesmon: binding to actin and myosin and effects on elementary steps in the ATPase cycle

Caldesmon: binding to actin and myosin and effects on elementary steps in the ATPase cycle

Dimethyl sulphoxide enhances the effects of Pi in myofibrils and inhibits the activity of rabbit skeletal muscle contractile proteins

Structural Characterization of Weakly Attached Cross-Bridges in the A·M·ATP State in Permeabilized Rabbit Psoas Muscle

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