Cross‐bridge kinetics in the presence of MgADP investigated by photolysis of caged ATP in rabbit psoas muscle fibres.

Dantzig, Jody A.; Hibberd, Mark G.; Trentham, David R.; Goldman, Yale E.

doi:10.1113/jphysiol.1991.sp018405

Cited by 139 publications

(152 citation statements)

References 49 publications

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“…At saturating ADP the reaction observed is A* ϩ M.ADP 3 AM.ADP: we still observe no working stroke and as M.ADP has been assigned to being in a rigor conformation, so must AM.ADP. This observation is in agreement with structural studies for myosin II (19), although it must be acknowledged that fiber studies have suggested that a small lever movement could still control the rate of ADP release (20). Actin binds to M.ADP and forms a weakly bound complex that Geeves (21) labeled A-MD (an A state).…”

Section: Discussionsupporting

confidence: 84%

The working stroke upon myosin–nucleotide complexes binding to actin

Walter

Smith

Sleep

2003

Proc. Natl. Acad. Sci. U.S.A.

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For many years, it has been known that myosin binds to actin tightly, but it had not been possible to devise a muscle fiber experiment to determine whether this binding energy is directly coupled to the working stroke of the actomyosin crossbridge cycle. Addressing the question at the single-molecule level with optical tweezers allows the problem to be resolved. We have compared the working stroke on the binding of four myosin complexes (myosin, myosin-ADP, myosin-pyrophosphate, and myosin-adenyl5yl imidodiphosphate) with that observed while hydrolyzing ATP. None of the four was observed to give a working stroke significantly different from zero. A working stroke (5.4 nm) was observed only with ATP, which indicates that the other states bind to actin in a rigor-like conformation and that myosin products (M.ADP.Pi), the state that binds to actin during ATPase activity, binds in a different, prestroke conformation. We conclude that myosin, while dissociated from actin, must be able to take up at least two mechanical conformations and show that our results are consistent with these conformations corresponding to the two states characterized at high resolution, which are commonly referred to in terms of having open and closed nucleotide binding pockets. E vidence from electron micrographs for different conformations of myosin led to the rowing model of actomyosin (AM) crossbridge action (1, 2) in which myosin binds to actin in one conformation, undergoes a working stroke, and detaches in a second conformation. The Lymn-Taylor scheme (3) describing the biochemical kinetics of AM provided a natural match to the mechanical model (Fig. 1). The detached myosin products (M.ADP.P i ) state bound to actin, and the working stroke occurred in association with product release. The binding of ATP facilitated dissociation of actin, and its hydrolysis took place while myosin was dissociated. The model postulated that the hydrolysis step is associated with repriming the head from the postpower-stroke structure back to the prepower-stroke form, although there was no evidence on this point at the time. Based on the observation that the detached states, myosin-ATP and M.ADP.P i , behaved in a similar manner with respect to actin binding, Eisenberg and collaborators (4) favored a model in which there was a single detached conformation of myosin.Measurement of the ATP binding constant (5) and the actin binding constant (6) were crucial steps in allowing the basic energetics of the AM mechanism to be elucidated. Much of the free energy of ATP hydrolysis is associated with actin binding to the M.ADP.P i state and forming the rigor AM state (7), the part of the scheme that must encompass the working stroke. The myosin state in the absence of nucleotide binds even more tightly to actin, and if it is the energy of AM binding that powers the mechanical action, it would suggest that a working stroke would also result from myosin binding to actin. This idea is consistent with the views of Eisenberg (4) and the ''3G'' model of contraction (8). ...

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Section: Discussionsupporting

confidence: 84%

The working stroke upon myosin–nucleotide complexes binding to actin

Walter

Smith

Sleep

2003

Proc. Natl. Acad. Sci. U.S.A.

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“…5A), although the tension rise in the presence of ADP was indeed earlier and slower than control. Also, Dantzig et al (1991), who were the first to point out the ADP-related early tension rise in psoas fibres at room temperature, did not notice the biphasic nature of the contraction. However, if the experimental temperature is lowered to 8°C, even the psoas fibres exhibit clear biphasic contractions in the presence of ADP (Horiuti et al 1994b).…”

Section: Binding Of Little Adp To the Cycling Cross-bridgementioning

confidence: 97%

“…The affinity of ADP for the rigor cross-bridge was directly examined (without using caged ATP) by studying the relaxing effect of ADP on the rigor fibre (Dantzig, Hibberd, Trentham & Goldman, 1991). Figure 9A shows a typical chart record from the ADP titration experiments.…”

Section: Km For Adp Of the Rigor Cross-bridgementioning

confidence: 99%

“…(iii) Its magnitude is not dependent on the size of the pre-ATP rigor tension (Horiuti et al 1994b). The mechanism underlying the early tension development is but poorly understood, although several hypotheses have been proposed (Dantzig et al 1991;Horiuti et al 1994b;Thirlwell et al 1994). Among others a recent hypothesis by Thomas & Thornhill (1995) is worth mentioning here.…”

Section: Binding Of Little Adp To the Cycling Cross-bridgementioning

confidence: 99%

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Mechanical study of rat soleus muscle using caged ATP and X‐ray diffraction: high ADP affinity of slow cross‐bridges

Horiuti

Yagi

Takemori

1997

The Journal of Physiology

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The cross‐bridges in slow‐ and fast‐twitch fibres (taken, respectively, from soleus and psoas muscles of rats) were examined in mechanical experiments using caged ATP and X‐ray diffraction, to compare their binding of ATP and ADP. Caged ATP was photolysed in rigor fibres. When ADP was removed from pre‐photolysis fibres, the initial relaxation (±Ca2+) in soleus was as fast as that in psoas fibres, whereas the subsequent contraction (+Ca2+) was slower in soleus than in psoas. The ATPase rate during the steady‐state contraction was also slower in soleus fibres. When ADP was added to pre‐photolysis fibres (±Ca2+), tension developed even in the initial phase, the overall tension development being biphasic. Both initial and late components of the Ca2+‐free contraction were enhanced when ADP was added before photolysis, although pre‐photolysis ADP was not a prerequisite for the late component. The effect of ADP was greater in soleus than in psoas fibres. Static experiments on rigor fibres revealed a higher ADP affinity in soleus fibres. The intensity of the actin layer‐line from ADP rigor soleus fibres decreased rapidly on photorelease of ATP. We conclude that, despite the tight ADP binding of the soleus cross‐bridge, its isometric reaction is not rate limited by the ‘off’ rate of ADP.

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“…Direct evidence for strain-limited ADP-release (or ATP binding) has been hard to come by for fast muscle myosins (but see Dantzig et al 1991). However, it is clear that ADP release can be important in timing cross-bridge detachment.…”

Section: Introductionmentioning

confidence: 99%

Adenosine diphosphate and strain sensitivity in myosin motors

Nyitrai

Geeves

2004

Phil. Trans. R. Soc. Lond. B

169

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The release of adenosine diphosphate (ADP) from the actomyosin cross-bridge plays an important role in the adenosine-triphosphate-driven cross-bridge cycle. In fast contracting muscle fibres, the rate at which ADP is released from the cross-bridge correlates with the maximum shortening velocity of the muscle fibre, and in some models the rate of ADP release defines the maximum shortening velocity. In addition, it has long been thought that the rate of ADP release could be sensitive to the load on the cross-bridge and thereby provide a molecular explanation of the Fenn effect. However, direct evidence of a strain-sensitive ADPrelease mechanism has been hard to come by for fast muscle myosins. The recently published evidence for a strain-sensing mechanism involving ADP release for slower muscle myosins, and in particular non-muscle myosins, is more compelling and can provide the mechanism of processivity for motors such as myosin V. It is therefore timely to examine the evidence for this strain-sensing mechanism. The evidence presented here will argue that a strain-sensitive mechanism of ADP release is universal for all myosins but the basic mechanism has evolved in different ways for different types of myosin. Furthermore, this strain-sensing mechanism provides a way of coordinating the action of multiple myosin motor domains in a single myosin molecule, or in complex assemblies of myosins over long distances without invoking a classic direct allosteric or cooperative communication between motors.

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Cross‐bridge kinetics in the presence of MgADP investigated by photolysis of caged ATP in rabbit psoas muscle fibres.

Cited by 139 publications

References 49 publications

The working stroke upon myosin–nucleotide complexes binding to actin

The working stroke upon myosin–nucleotide complexes binding to actin

Mechanical study of rat soleus muscle using caged ATP and X‐ray diffraction: high ADP affinity of slow cross‐bridges

Adenosine diphosphate and strain sensitivity in myosin motors

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