scholarly journals Recent X-ray Diffraction and Electron Microscope Studies of Striated Muscle

1967 ◽  
Vol 50 (6) ◽  
pp. 71-83 ◽  
Author(s):  
H. E. Huxley
Keyword(s):  
Active Sites ◽  
Striated Muscle ◽  
Structural Features ◽  
Actin Binding ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thick Filaments ◽  
Myosin Filaments ◽  
The Cross ◽  
Cross Bridges

The sliding filament model for muscular contraction supposes that an appropriately directed force is developed between the actin and myosin filaments by some process in which the cross-bridges are involved. The cross-bridges between the filaments are believed to represent the parts of the myosin molecules which possess the active sites for ATPase activity and actin-binding ability, and project out sidewise from the backbone of the thick filaments. The arrangement of the cross-bridges is now being studied by improved low-angle X-ray diffraction techniques, which show that in a resting muscle, they are arranged approximately but not exactly in a helical pattern, and that there are other structural features of the thick filaments which give rise to additional long periodicities shown up by the X-ray diagram. The actin filaments also contain helically arranged subunits, and both the subunit repeat and the helical repeat are different from those in the myosin filaments. Diffraction diagrams can be obtained from muscles in rigor (when permanent attachment of the cross-bridges to the actin subunits takes place) and now, taking advantage of the great increase in the speed of recording, from actively contracting muscles. These show that changes in the arrangement of the cross-bridges are produced under both these conditions and are no doubt associated in contraction with the development of force. Thus configurational changes of the myosin component in muscle have been demonstrated: these take place without any significant over-all change in the length of the filaments.

scholarly journals Myosin Cross-Bridge Behaviour in Contracting Muscle—The T1 Curve of Huxley and Simmons (1971) Revisited

2019 ◽  
Vol 20 (19) ◽  
pp. 4892 ◽  
Author(s):  
Knupp ◽  
Squire
Keyword(s):  
Actin Filaments ◽  
Striated Muscle ◽  
Reliable Estimate ◽  
X Ray Diffraction ◽  
Step Size ◽  
X Ray ◽  
Cross Bridge ◽  
Length Changes ◽  
The Cross ◽  
Cross Bridges

The stiffness of the myosin cross-bridges is a key factor in analysing possible scenarios to explain myosin head changes during force generation in active muscles. The seminal study of Huxley and Simmons (1971: Nature 233: 533) suggested that most of the observed half-sarcomere instantaneous compliance (=1/stiffness) resides in the myosin heads. They showed with a so-called T1 plot that, after a very fast release, the half-sarcomere tension reduced to zero after a step size of about 60Å (later with improved experiments reduced to 40Å). However, later X-ray diffraction studies showed that myosin and actin filaments themselves stretch slightly under tension, which means that most (at least two-thirds) of the half sarcomere compliance comes from the filaments and not from cross-bridges. Here we have used a different approach, namely to model the compliances in a virtual half sarcomere structure in silico. We confirm that the T1 curve comes almost entirely from length changes in the myosin and actin filaments, because the calculated cross-bridge stiffness (probably greater than 0.4 pN/Å) is higher than previous studies have suggested. Our model demonstrates that the formulations produced by previous authors give very similar results to our model if the same starting parameters are used. However, we find that it is necessary to model the X-ray diffraction data as well as mechanics data to get a reliable estimate of the cross-bridge stiffness. In the light of the high cross-bridge stiffness found in the present study, we present a plausible modified scenario to describe aspects of the myosin cross-bridge cycle in active muscle. In particular, we suggest that, apart from the filament compliances, most of the cross-bridge contribution to the instantaneous T1 response may come from weakly-bound myosin heads, not myosin heads in strongly attached states. The strongly attached heads would still contribute to the T1 curve, but only in a very minor way, with a stiffness that we postulate could be around 0.1 pN/Å, a value which would generate a working stroke close to 100 Å from the hydrolysis of one ATP molecule. The new model can serve as a tool to calculate sarcomere elastic properties for any vertebrate striated muscle once various parameters have been determined (e.g., tension, T1 intercept, temperature, X-ray diffraction spacing results).

An ultrastructural study of crossbridge arrangement in the fish skeletal muscle thick filament

1989 ◽  
Vol 94 (3) ◽  
pp. 391-401
Author(s):  
R.W. Kensler ◽  
M. Stewart
Keyword(s):  
Skeletal Muscle ◽  
Fourier Transforms ◽  
Thick Filament ◽  
Fish Muscle ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thick Filaments ◽  
Gold Fish ◽  
Diffraction Patterns ◽  
Cross Bridges

A procedure has been developed for isolating gold-fish skeletal muscle thick filaments that preserves the near-helical arrangement of the myosin cross-bridges under relaxing conditions. These filaments have been examined by electron microscopy and computer image analysis. Electron micrographs of the negatively stained filaments showed a clear periodicity associated with the crossbridges, with an axial repeat every 42.9 nm. Computed Fourier transforms of the negatively stained filaments showed a series of layer lines confirming this periodicity, and were similar to the X-ray diffraction patterns of fish muscle obtained by J. Hartford and J. Squire. Analysis of the computed transform data and filtered images of the isolated fish filaments demonstrated that the myosin crossbridges lie along three strands. Platinum shadowing demonstrated that the strands have a right-handed orientation, and computed transforms and filtered images of the shadowed filaments suggest that the crossbridges are perturbed both axially and azimuthally from an ideal helical arrangement.

scholarly journals Resting myosin cross-bridge configuration in frog muscle thick filaments.

1986 ◽  
Vol 102 (2) ◽  
pp. 610-618 ◽  
Author(s):  
M Cantino ◽  
J Squire
Keyword(s):  
Myosin Head ◽  
Freeze Fracture ◽  
Optical Diffraction ◽  
Outer Diameter ◽  
X Ray ◽  
Cross Bridge ◽  
Thick Filaments ◽  
Myosin Filaments ◽  
Cross Bridges ◽  
The Right

Clear images of myosin filaments have been seen in shadowed freeze-fracture replicas of single fibers of relaxed frog semitendinosus muscles rapidly frozen using a dual propane jet freezing device. These images have been analyzed by optical diffraction and computer averaging and have been modelled to reveal details of the myosin head configuration on the right-handed, three-stranded helix of cross-bridges. Both the characteristic 430-A and 140-150-A repeats of the myosin cross-bridge array could be seen. The measured filament backbone diameter was 140-160 A, and the outer diameter of the cross-bridge array was 300 A. Evidence is presented that suggests that the observed images are consistent with a model in which both of the heads of one myosin molecule tilt in the same direction at an angle of approximately 50-70 degrees to the normal to the filament long axis and are slewed so that they lie alongside each other and their radially projected density lies along the three right-handed helical tracks. Any perturbation of the myosin heads away from their ideal lattice sites needed to account for x-ray reflections not predicted for a perfect helix must be essentially along the three helical tracks of cross-bridges. Little trace of the presence of non-myosin proteins could be seen.

scholarly journals An electron microscopic and optical diffraction analysis of the structure of Limulus telson muscle thick filaments.

1982 ◽  
Vol 92 (2) ◽  
pp. 443-451 ◽  
Author(s):  
R W Kensler ◽  
R J Levine
Keyword(s):  
Electron Microscopy ◽  
Diffraction Analysis ◽  
Electron Micrographs ◽  
Optical Diffraction ◽  
X Ray Diffraction ◽  
Electron Microscopic ◽  
X Ray ◽  
Thick Filaments ◽  
Diffraction Patterns ◽  
Cross Bridges

Long, thick filaments (greater than 4.0 micrometer) rapidly and gently isolated from fresh, unstimulated Limulus muscle by an improved procedure have been examined by electron microscopy and optical diffraction. Images of negatively stained filaments appear highly periodic with a well-preserved myosin cross-bridge array. Optical diffraction patterns of the electron micrographs show a wealth of detail and are consistent with a myosin helical repeat of 43.8 nm, similar to that observed by x-ray diffraction. Analysis of the optical diffraction patterns, in conjunction with the appearance in electron micrographs of the filaments, supports a model for the filament in which the myosin cross-bridges are arranged on a four-stranded helix, with 12 cross-bridges per turn or each helix, thus giving an axial repeat every third level of cross-bridges (43.8 nm).

scholarly journals Structural changes induced in Ca2+-regulated myosin filaments by Ca2+ and ATP.

1989 ◽  
Vol 109 (2) ◽  
pp. 529-538 ◽  
Author(s):  
L L Frado ◽  
R Craig
Keyword(s):  
Structural Changes ◽  
Striated Muscle ◽  
Structural Basis ◽  
Ordered Structure ◽  
Compact Structure ◽  
Crude Homogenate ◽  
Myosin Filaments ◽  
The Cross ◽  
Cross Bridges ◽  
Muscle Myosin

We have used electron microscopy and proteolytic susceptibility to study the structural basis of myosin-linked regulation in synthetic filaments of scallop striated muscle myosin. Using papain as a probe of the structure of the head-rod junction, we find that this region of myosin is approximately five times more susceptible to proteolytic attack under activating (ATP/high Ca2+) or rigor (no ATP) conditions than under relaxing conditions (ATP/low Ca2+). A similar result was obtained with native myosin filaments in a crude homogenate of scallop muscle. Proteolytic susceptibility under conditions in which ADP or adenosine 5'-(beta, gamma-imidotriphosphate) (AMPPNP) replaced ATP was similar to that in the absence of nucleotide. Synthetic myosin filaments negatively stained under relaxing conditions showed a compact structure, in which the myosin cross-bridges were close to the filament backbone and well ordered, with a clear 14.5-nm axial repeat. Under activating or rigor conditions, the cross-bridges became clumped and disordered and frequently projected further from the filament backbone, as has been found with native filaments; when ADP or AMPPNP replaced ATP, the cross-bridges were also disordered. We conclude (a) that Ca2+ and ATP affect the affinity of the myosin cross-bridges for the filament backbone or for each other; (b) that the changes observed in the myosin filaments reflect a property of the myosin molecules alone, and are unlikely to be an artifact of negative staining; and (c) that the ordered structure occurs only in the relaxed state, requiring both the presence of hydrolyzed ATP on the myosin heads and the absence of Ca2+.

High-Resolution X-ray Diffraction of Muscle Using Undulator Radiation from the Tristan Main Ring at KEK

1998 ◽  
Vol 5 (3) ◽  
pp. 280-285 ◽  
Author(s):  
Katsuzo Wakabayashi ◽  
Hiroshi Sugiyama ◽  
Naoto Yagi ◽  
Thomas C. Irving ◽  
Hiroyuki Iwamoto ◽  
...  
Keyword(s):  
High Resolution ◽  
Striated Muscle ◽  
Operating Conditions ◽  
High Angular Resolution ◽  
X Ray Diffraction ◽  
Undulator Radiation ◽  
X Ray ◽  
Thick Filaments ◽  
Main Ring ◽  
Static Conditions

High-resolution X-ray diffraction studies on striated muscle fibres were performed using a hard X-ray undulator installed in the Tristan main ring at KEK, Tsukuba, Japan. The performance of the undulator, along with an example experiment which exploited the unique characteristics of undulator radiation, are reported. The vertical divergence angle of the first harmonic of the undulator was ∼10 µrad under 8 GeV multi-bunch operating conditions and the peak photon flux density was estimated to be ∼3 × 1016 photons s−1 mrad−2 (0.1% bandwidth)−1 (10 mA)−1. The well collimated X-ray beam from the undulator made it possible to resolve clearly, with high angular resolution (∼700 nm), the closely spaced diffraction peaks on the meridional axis in the X-ray patterns arising from the thick filaments of a striated muscle under static conditions. By fitting the meridional intensity pattern, a model for the molecular arrangement of the constituent proteins in the thick filaments is proposed. These studies of muscle demonstrate the promise of undulator radiation from third-generation sources for high-resolution diffraction studies.

scholarly journals LOCUS AND STATE OF AGGREGATION OF MYOSIN IN TISSUE SECTIONS OF VERTEBRATE SMOOTH MUSCLE

1970 ◽  
Vol 44 (1) ◽  
pp. 52-61 ◽  
Author(s):  
Bernard J. Panner ◽  
Carl R. Honig
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscles ◽  
Smooth Muscle Contraction ◽  
Low Ph ◽  
X Ray Diffraction ◽  
X Ray ◽  
Tissue Sections ◽  
Thick Filaments ◽  
Myosin Filaments ◽  
And Storage

Structures with the characteristics of molecular myosin were identified by electron microscopy in tissue sections of vertebrate smooth muscle. No thick filaments of myosin were found regardless of preparative procedures, which included fixation at rest and in contraction, glycerine extraction, and storage at low pH prior to fixation. Absence of thick myosin filaments and presence of what appear to be myosin molecules is in accord with conclusions based on X-ray diffraction (3, 12) and birefringence data (4) from living smooth muscles at rest and in contraction. Explanations are provided for appearances thought by others (6, 20, 21) to represent thick myosin filaments. Our present observations are in accord with the model for smooth muscle contraction which we have previously proposed (1).

scholarly journals Myosin Cross-bridge Behaviour in Contracting Muscle – The T1 Curve of Huxley & Simmons (1971) Revisited

2019 ◽  
Author(s):  
Carlo Knupp ◽  
John M. Squire
Keyword(s):  
Actin Filaments ◽  
Striated Muscle ◽  
X Ray Diffraction ◽  
Step Size ◽  
Weakly Bound ◽  
X Ray ◽  
Cross Bridge ◽  
Key Factor ◽  
Length Changes ◽  
Cross Bridges

The stiffness of the myosin cross-bridges is a key factor in analysing possible scenarios to explain myosin head changes during force generation in active muscles.  The seminal study of Huxley and Simmons (1971: Nature 233: 533) suggested that most of the observed half-sarcomere instantaneous compliance (=1/stiffness) resides in the myosin heads.    They showed with a so-called T1 plot that, after a very fast release, the half-sarcomere tension reduced to zero after a step size of about 60Å (later with improved experiments reduced to 40Å).   However, later X-ray diffraction studies showed that myosin and actin filaments themselves stretch slightly under tension, which means that most (at least two-thirds) of the half sarcomere compliance comes from the filaments and not from cross-bridges.    Here we have used a different approach, namely to model the compliances in a virtual half sarcomere structure in silico.   We confirm that the T1 curve comes almost entirely from length changes in the myosin and actin filaments, because the calculated cross-bridge stiffness (probably greater than 0.4 pN/Å) is higher than previous studies have suggested.    In the light of this, we present a plausible modified scenario to describe aspects of the myosin cross-bridge cycle in active muscle.   In particular, we suggest that, apart from the filament compliances, most of the cross-bridge contribution to the instantaneous T1 response comes from weakly-bound myosin heads, not myosin heads in strongly attached states.   The strongly attached heads would still contribute to the T1 curve, but only in a very minor way, with a stiffness that we postulate could be around 0.1 pN/Å, a value which would generate a working stroke close to 100 Å from the hydrolysis of one ATP molecule.  The new program can serve as a tool to calculate sarcomere elastic properties for any vertebrate striated muscle once various parameters have been determined (e.g. tension, T1 intercept, temperature, X-ray diffraction spacing results).

scholarly journals The vertebrate skeletal muscle thick filaments are not three-stranded. Reinterpretation of some experimental data.

2002 ◽  
Vol 49 (4) ◽  
pp. 841-853 ◽  
Author(s):  
Ludmila Skubiszak ◽  
Leszek Kowalczyk
Keyword(s):  
Skeletal Muscle ◽  
Mass Distribution ◽  
Thick Filament ◽  
X Ray Diffraction ◽  
Bipolar Structure ◽  
X Ray ◽  
Thick Filaments ◽  
Diffraction Patterns ◽  
Cross Bridges ◽  
Vertebrate Skeletal Muscle

Computer simulation of mass distribution within the model and Fourier transforms of images depicting mass distribution are explored for verification of two alternative modes of the myosin molecule arrangement within the vertebrate skeletal muscle thick filaments. The model well depicting the complete bipolar structure of the thick filament and revealing a true threefold-rotational symmetry is a tube covered by two helices with a pitch of 2 x 43 nm due to arrangement of the myosin tails along a helical path and grouping of all myosin heads in the crowns rotated by 240 degrees and each containing three cross-bridges separated by 0 degrees, 120 degrees, and 180 degrees. The cross-bridge crown parameters are verified by EM images as well as by optical and low-angle X-ray diffraction patterns found in the literature. The myosin tail arrangement, at which the C-terminus of about 43-nm length is near-parallel to the filament axis and the rest of the tail is quite strongly twisted around, is verified by the high-angle X-ray diffraction patterns. A consequence of the new packing is a new way of movement of the myosin cross-bridges, namely, not by bending in the hinge domains, but by unwrapping from the thick filament surface towards the thin filaments along a helical path.

Distribution of c-protein isoforms in sarcomeres of developing chick skeletal muscle

1988 ◽  
Vol 46 ◽  
pp. 226-227
Author(s):  
D. A. Fischman ◽  
J. E. Dennis ◽  
T. Obinata ◽  
H. Takano-Ohmuro
Keyword(s):  
Skeletal Muscles ◽  
Thick Filament ◽  
Protein Isoforms ◽  
Actin Binding ◽  
Striated Muscles ◽  
C Protein ◽  
Sarcomeric Protein ◽  
Thick Filaments ◽  
Cross Bridges ◽  
Bridge Bearing

C-protein is a 150 kDa protein found within the A bands of all vertebrate cross-striated muscles. By immunoelectron microscopy, it has been demonstrated that C-protein is distributed along a series of 7-9 transverse stripes in the medial, cross-bridge bearing zone of each A band. This zone is now termed the C-zone of the sarcomere. Interest in this protein has been sparked by its striking distribution in the sarcomere: the transverse repeat between C-protein stripes is 43 nm, almost exactly 3 times the 14.3 nm axial repeat of myosin cross-bridges along the thick filaments. The precise packing of C-protein in the thick filament is still unknown. It is the only sarcomeric protein which binds to both myosin and actin, and the actin-binding is Ca-sensitive. In cardiac and slow, but not fast, skeletal muscles C-protein is phosphorylated. Amino acid composition suggests a protein of little or no αhelical content. Variant forms (isoforms) of C-protein have been identified in cardiac, slow and embryonic muscles.

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