Fraction of myosin heads bound to thin filaments in rigor fibrils from insect flight and vertebrate muscles

Lovell, Stephen J.; Knight, Peter J.; Harrington, William F.

doi:10.1038/293664a0

Cited by 78 publications

(47 citation statements)

References 10 publications

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“…The experimental results show that even at full filament overlap, 25% of the myosin heads bind AdoPP[NH]P with a binding constant greater than 3 x lo6 M-', similar to the affinity for rabbit myosin heads not overlapped by actin. This is consistent with the observations that 25 -30% of the myosin heads in fully overlapped insect fibrils do not interact with actin even in rigor [17,181. The remaining heads in Lethocerus, presumably interacting with actin, bind AdoPP[NH]P with an association constant of 8 x lo3 M-', which is 8 times stronger than the association constant observed for rabbit myosin heads over-lapped with actin, and is in agreement with the association constant observed for AdoPP[NH]P originally determined using Lethocerus flight muscle fibers [15, 161.…”

supporting

confidence: 81%

“…Love11 et al [17] using SDS gel patterns of tryptic digests of Sarcophaga fibrils to measure the intensity of the 160-kDa myosin fragment bound in rigor, relative to the amount bound in 2 mM magnesium pyrophosphate, calculated that 70% of the myosin heads were bound to actin in rigor. Goody et al [I81 suggested from measurements of the binding of exogenous myosin subfragment 1 to Lethocerus fibers by quantitative SDS/PAGE, X-ray diffraction, interference microscopy, and electron microscopy that 75% of the endogenous myosin heads were attached to actin in insect rigor.…”

Section: Discussionmentioning

confidence: 99%

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Binding of ADP and adenosine 5′‐[β,γ‐imido]triphosphate to insect flight muscle fibrils

Biosca

Eisenberg

Reedy

et al. 1990

European Journal of Biochemistry

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We have studied the binding of ADP and adenosine 5'-[/?,y-imido]triphosphate (AdoPP[NH]P) to insect flight muscle fibrils. We find that 25% of the myosin heads, presumably those which do not interact with actin, bind AdoPP[NH]P with a binding constant greater than 3 x lo6 M-', similar to the binding constant of the same compound to the rabbit myosin heads which do not overlap with actin. The remaining heads in insect myofibrils bind AdoPP[NH]P with an association constant of 8 x lo3 M-', which is eight times stronger than the affinity of this compound for rabbit myosin heads in overlap with actin. Therefore, in contrast to the situation with rabbit myofibrils where AdoPP[NH]P binds much more weakly than ADP, with insect myofibrils these two adenosine phosphates bind with almost equal affinity. This is consistent with the numerous structural studies on insect flight muscle which were interpreted on the basis that most of the actomyosin sites were saturated with nucleotide at an AdoPP[NH]P concentration of 1 mM.The highly regular structure of insect fibrillar flight muscle has made it useful for X-ray diffraction and electron microscopy studies of myosin crossbridge conformation in the presence and absence of nucleotides [l, 21. The most extensively studied condition occurs in the absence of ATP [3 -51 ; this rigor state is widely used as a model for the end of the crossbridge power stroke (the 45" state). The beginning of the power stroke has been modeled after the 90" detached crossbridges seen in Lethocerus muscle relaxed by ATP [3, 61. Attempts to visualize intermediate crossbridge conformations have centered around the use of nucleotide analogs to trap myosin heads at some position between the 90" and 45" states. Adenosine 5'-[P,y-imido]triphosphate (AdoPP[NH]P), an ATP analog not hydrolyzed by myosin [7], is the most widely used of these analogs [8,9] because it causes a large drop in rigor tension without reducing stiffness. This suggests that a large number of crossbridges remain attached but are caught at a different part of the crossbridge stroke. In Lethocerus flight muscle the structure resulting from exposure to AdoPP[NH]P at 4 "C defies simple interpretation because, in the cold, AdoPP[NH]P induces a mixed structural state in which attached crossbridges are altered by the analogue and show both rigor and relaxed features. In addition, although muscles from other species show a drop in tension with constant stiffness in the presence of AdoPP[NH]P, structural responses are varied [lo] or even undetectable 1111.Moreover, the binding of AdoPP[NH]P shows a strong dependence on whether or not the myosin head is bound to

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supporting

confidence: 81%

Section: Discussionmentioning

confidence: 99%

Binding of ADP and adenosine 5′‐[β,γ‐imido]triphosphate to insect flight muscle fibrils

Biosca

Eisenberg

Reedy

et al. 1990

European Journal of Biochemistry

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“…To estimate the proportion of attached crossbridges, we compared the stiffness (change of force in response to a quick length change) in the active muscle fiber to that of the muscle fiber in rigor (32), where all the crossbridges are thought to be attached (33)(34)(35). In the red and white fibers, a quick stretch of a fiber in active contraction produced a force change only slightly lower than in rigor (Fig.…”

Section: Resultsmentioning

confidence: 99%

Trading force for speed: Why superfast crossbridge kinetics leads to superlow forces

Rome

Cook

Syme

et al. 1999

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

127

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Superfast muscles power high-frequency motions such as sound production and visual tracking. As a class, these muscles also generate low forces. Using the toadfish swimbladder muscle, the fastest known vertebrate muscle, we examined the crossbridge kinetic rates responsible for high contraction rates and how these might affect force generation. Swimbladder fibers have evolved a 10-fold faster crossbridge detachment rate than fast-twitch locomotory fibers, but surprisingly the crossbridge attachment rate has remained unchanged. These kinetics result in very few crossbridges being attached during contraction of superfast fibers (only Ϸ1͞6 of that in locomotory fibers) and thus low force. This imbalance between attachment and detachment rates is likely to be a general mechanism that imposes a tradeoff of force for speed in all superfast fibers.The superfast fiber type is found where high-frequency contractions are required, such as in vertebrate eye muscles and in both vertebrate and invertebrate synchronous soundproducing muscles. These muscles have a series of modifications for speed, including a large volume of sarcoplasmic reticulum (SR) (1-7) to produce very rapid calcium transients (8) and low-affinity troponin to speed myofilament deactivation after [Ca 2ϩ

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“…4B) for intact, trypsin-treated, calpain-treated myofibrils in a rigor state but no corresponding ruptures were observed for myofibrils in a relaxed state. As all myosin heads were attached to and detached from actin filaments in rigor and relaxed myofibrils, respectively (Cooke and Franks, 1980;Lovell et al, 1981) and as the tensile force required to break a rigor complex is about 15 pN (Nishizaka et al, 2000), these 5-20 pN ruptures may have come from breakings of the rigor complexes formed in myofibrils. Similarly, in the AFM experiments (Fig.…”

Section: Characteristic Ruptures Of Peripheral Components Of Myofibrilsmentioning

confidence: 99%

Mechanical Strength of Sarcomere Structures of Skeletal Myofibrils Studied by Submicromanipulation

Kayamori

Miyake

Akiyama

et al. 2006

Cell Struct. Funct.

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ABSTRACT. The mechanical strength of sarcomere structures of skeletal muscle was studied by rupturing single myofibrils of rabbit psoas muscle by submicromanipulation techniques. Microbeads coated with α-actinin were attached to the surface of myofibrils immobilized to coverslip. By use of either optical tweezers or atomic force microscope, the attached beads were captured and detached from the myofibrils. During the detachment of the beads, the actin filaments bound specifically to the beads were peeled off from the bulk structures of myofibrils, thus rupturing the peripheral components of the myofibrils bound to the actin filaments. By analyzing the ruptures thus produced in various myofibril preparations, it was found that the sarcomere structure of myofibrils is maintained by numerous molecular components having the mechanical strength sufficient to sustain the contractile force produced by the actomyosin system. The present techniques could be applied to study the mechanical strength of cellular organelles containing actin filaments as their component.

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Fraction of myosin heads bound to thin filaments in rigor fibrils from insect flight and vertebrate muscles

Cited by 78 publications

References 10 publications

Binding of ADP and adenosine 5′‐[β,γ‐imido]triphosphate to insect flight muscle fibrils

Binding of ADP and adenosine 5′‐[β,γ‐imido]triphosphate to insect flight muscle fibrils

Trading force for speed: Why superfast crossbridge kinetics leads to superlow forces

Mechanical Strength of Sarcomere Structures of Skeletal Myofibrils Studied by Submicromanipulation

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