Intensities Of Layer Lines Research Articles

Fast skeletal myosin-binding protein-C regulates fast skeletal muscle contraction

Fast skeletal myosin-binding protein-C (fMyBP-C) is one of three MyBP-C paralogs and is predominantly expressed in fast skeletal muscle. Mutations in the gene that encodes fMyBP-C, MYBPC2, are associated with distal arthrogryposis, while loss of fMyBP-C protein is associated with diseased muscle. However, the functional and structural roles of fMyBP-C in skeletal muscle remain unclear. To address this gap, we generated a homozygous fMyBP-C knockout mouse (C2-/-) and characterized it both in vivo and in vitro compared to wild-type mice. Ablation of fMyBP-C was benign in terms of muscle weight, fiber type, cross-sectional area, and sarcomere ultrastructure. However, grip strength and plantar flexor muscle strength were significantly decreased in C2-/- mice. Peak isometric tetanic force and isotonic speed of contraction were significantly reduced in isolated extensor digitorum longus (EDL) from C2-/- mice. Small-angle X-ray diffraction of C2-/- EDL muscle showed significantly increased equatorial intensity ratio during contraction, indicating a greater shift of myosin heads toward actin, while MLL4 layer line intensity was decreased at rest, indicating less ordered myosin heads. Interfilament lattice spacing increased significantly in C2-/- EDL muscle. Consistent with these findings, we observed a significant reduction of steady-state isometric force during Ca2+-activation, decreased myofilament calcium sensitivity, and sinusoidal stiffness in skinned EDL muscle fibers from C2-/- mice. Finally, C2-/- muscles displayed disruption of inflammatory and regenerative pathways, along with increased muscle damage upon mechanical overload. Together, our data suggest that fMyBP-C is essential for maximal speed and force of contraction, sarcomere integrity, and calcium sensitivity in fast-twitch muscle.

Myosin Head Configurations in Resting and Contracting Murine Skeletal Muscle.

Transgenic mouse models have been important tools for studying the relationship of genotype to phenotype for human diseases, including those of skeletal muscle. We show that mouse skeletal muscle can produce high quality X-ray diffraction patterns establishing the mouse intact skeletal muscle X-ray preparation as a potentially powerful tool to test structural hypotheses in health and disease. A notable feature of the mouse model system is the presence of residual myosin layer line intensities in contracting mouse muscle patterns. This provides an additional tool, along with the I1,1/I1,0 intensity ratio, for estimating the proportions of active versus relaxed myosin heads under a given set of conditions that can be used to characterize a given physiological condition or mutant muscle type. We also show that analysis of the myosin layer line intensity distribution, including derivation of the myosin head radius, Rm, may be used to study the role of the super-relaxed state in myosin regulation. When the myosin inhibitor blebbistatin is used to inhibit force production, there is a shift towards a highly quasi-helically ordered configuration that is distinct from the normal resting state, indicating there are more than one helically ordered configuration for resting crossbridges.

Deduction of the single-myosin-filament transforms from partially sampled layer lines in the X-ray diffraction pattern from vertebrate striated muscle

A novel method to correct a partial sampling effect, due to the hexagonal filament array of a statistical superlattice form, on the thick (myosin)-filament-based layer lines in X-ray diffraction patterns from higher-vertebrate striated muscle has been developed using the cylindrically averaged difference Patterson function [ΔQ(r, z)]. The method involves cutting off the inter-filament vector peaks that appear in the radial region beyond ∼32 nm on the ΔQ(r, z) map calculated from the observed layer-line intensities, and then deducing the single-myosin-filament transforms by inverse Fourier transformation of the truncated ΔQ(r, z). The accuracy of the cut-off method was tested using a single-myosin-filament model and a hexagonal filament-array model with a size of one superlattice unit cell. The layer-line intensities calculated from the truncated ΔQ(r, z) of the hexagonal filament-array model showed few sampling peaks, the layer lines being effectively coincident with those from the single-filament model except for the intensities close to the meridian. Some residual differences were caused by the face-to-face inter-crossbridge vectors between closest neighboring filaments, which correspond to ∼27.5% of the total number of crossbridge vectors in the truncated ΔQ(r, z) map, but the face-to-face inter-crossbridge vectors contributed mainly to the intensities close to the meridian. Their remnant off-meridional layer-line intensity components did not significantly affect a search for the optimum azimuthal orientation of myosin crossbridges in the resting state of muscle.

Different Orientation of Two Heads of a Myosin Crossbridge in Full-Filament Overlapped and Overstretched Muscles Obtained by X-Ray Fiber Diffraction

A novel method using the cylindrically averaged difference Patterson function was applied to correct a sampling effect due to the hexagonal filament array on the thick filament-based layer-line intensities from frog skeletal muscles at the full-filament overlap length. Using the corrected intensity data and the mixed structural model of a thick filament with two different axial periodicities of the myosin crossbridges, we performed an optimum search of azimuthal orientation of two heads of a myosin crossbridge and compared the optimum orientation to that from muscles stretched beyond filament overlap reported previously. The result showed that the myosin crossbriges in the regular repeating region had a similar configuration in both muscles. Two heads of a myosin crossbridge formed a windmill-shape when seen from the top of the filament and one head of a myosin crossbridge seemed to be almost in contact with another head in a pair at an adjacent crown level along the filament axis. One head was toward the converter domain of the other head, similar to regulated myosin heads in Tarantula muscles in which the intramolecular head-head interaction occurs. In the perturbed region, however, myosin crossbridges had different configurations in these muscles. In top view, two heads of a myosin crossbridge showed a U-shape structure in the overstreched muscles while a cross-shape structure in muscles with the full-filament overlap. One myosin head seemed to be in contact with the other head at the same axial crown level. The models suggest that the disposition of two-headed myosin crossbridges is stabilized by the head-head interaction at same or different axial crown levels. Probably this would be related to the inhibition mechanism of actomyosin interaction in the relaxed muscles.

Insight into the actin-myosin motor from x-ray diffraction on muscle

The origin of reflections in the x-ray diffraction pattern from striated muscle and their use for understanding the structural organization of the contractile machinery are presented and discussed. Results of x-ray diffraction experiments obtained by a number of research groups using a variety of protocols revealed structural changes in contracting muscles which are interpreted in terms of molecular movements that underlie force generation. Some of these data are in line with the widely accepted 'lever arm' hypothesis which links force generation to a tilt of the light chain domain of the myosin head with respect to its motor domain. However, changes in the layer line intensities observed in response to various perturbations cannot be explained by tilting of the lever arm. Such changes, first revealed in response to temperature jumps, are interpreted as a transition of non-stereo-specifically attached myosin heads to a stereo-specifically bound state. The new 'roll and lock' model considers force-generation as a two-stage process: initial stereo-specific locking of myosin heads on actin is followed by the lever arm tilt.

Direct Modeling of X-Ray Diffraction Pattern from Contracting Skeletal Muscle

A direct modeling approach was used to quantitatively interpret the two-dimensional x-ray diffraction patterns obtained from contracting mammalian skeletal muscle. The dependence of the calculated layer line intensities on the number of myosin heads bound to the thin filaments, on the conformation of these heads and on their mode of attachment to actin, was studied systematically. Results of modeling are compared to experimental data collected from permeabilized fibers from rabbit skeletal muscle contracting at 5°C and 30°C and developing low and high isometric tension, respectively. The results of the modeling show that: i), the intensity of the first actin layer line is independent of the tilt of the light chain domains of myosin heads and can be used as a measure of the fraction of myosin heads stereospecifically attached to actin; ii), during isometric contraction at near physiological temperature, the fraction of these heads is ∼40% and the light chain domains of the majority of them are more perpendicular to the filament axis than in rigor; and iii), at low temperature, when isometric tension is low, a majority of the attached myosin heads are bound to actin nonstereospecifically whereas at high temperature and tension they are bound stereospecifically.

Structural study of a series of ethylene–tetrafluoroethylene copolymers with various ethylene contents, Part 1: Structure at room temperature investigated for uniaxially-oriented samples by an organized combination of 2D-WAXD/SAXS and IR/Raman spectra

The X-ray fiber diagrams, polarized infrared/Raman spectra, and small-angle X-ray scattering data have been successfully measured for a series of uniaxially-oriented ethylene (E)–tetrafluoroethylene (TFE) random copolymers. The difference in crystal structure and morphology has been investigated. All the samples of E/TFE copolymer were found to take the planar-zigzag conformation at room temperature except pure polytetrafluoroethylene case. The layer line intensities of the X-ray fiber diagram and the 00l reflection intensities were found to change systematically. From this, the E and TFE sequences were considered to be included commonly in a crystal lattice. The detailed investigation of the polarized infrared and Raman spectra allowed us to assign the bands to some characteristic structures. These can be used effectively in the study of structural changes occurring in the phase transition of these copolymer samples. The 2-dimensional small-angle X-ray scattering patterns were compared among the copolymers and the difference in stacked lamellar structure has been discussed.

Quantitative structural analysis of individual nanotubes by electron diffraction

A general method for quantitative structure analysis of individual, cylindrical, carbon nanotubes is described here. The method is based on electron diffraction of individual nanotubes and analysis using a combination of helical diffraction theory and diffraction geometry of the underlying lattice. Experimental recording of nanotube diffraction is achieved using a nanometer-sized electron beam. Procedures are developed for 1) the measurement of chiral angles in both single- and multi-wall nanotubes and 2) structure determination based on Bessel function fitting of layer line intensity oscillations. The accuracy of the method is demonstrated for the structure determination of a single- and double-wall carbon nanotubes and partial structural analysis of a multiwall carbon nanotube. The results show that the single-, double- and incommensurate multi-wall tubes are well described by the cylindrical tube model. However, a large Debye-Waller factor in the radial direction is obtained. The method developed here is general and can be applied to other cylindrical nanotubes.

Helical signature motif in the fibre diffraction patterns of random-walk chains

Helical geometry is one of the most dominant structural features in polypeptides, nucleic acids, carbohydrates and long-chain polymers in general. Structures of a large number of helical biomolecules and important non-biological polymers have been determined by fibre diffraction and helical diffraction theory. This paper reports on a study of fibre diffraction patterns calculated for two different on-lattice random-walk models of polymers, with no built-in helical features. It is noted that such on-lattice random walks are natural models for polymers with fixed monomer geometries and inter-monomer angles. The presence of layer-line intensities is observed, characteristic of fibre diffraction patterns from helices with an integral number of units per turn. It is shown that under certain circumstances, fibre diffraction patterns of helical objects may be difficult to distinguish from cylindrically-averaged fibre diffraction patterns of random walks on lattices with fixed angles. A simple correspondence is demonstrated between the parameters of a helix and a random-walk chain with equivalent fibre diffraction patterns. These results call for a critical examination of the way the helical diffraction theory is typically used: certain structures that have been modelled as helical might, under some circumstances, be more naturally described as random-walk chains with no preferred conformation even on the shortest length-scale and in the context of a fibre.

Effects of solution tonicity on crossbridge properties and myosin lever arm disposition in intact frog muscle fibres

The aims of this study were to investigate the effects of solution tonicity on muscle properties, and to verify their consistence with the lever arm theory of force generation. Experiments were made in single muscle fibres and in fibre bundles from the frog, using both fast stretches and time-resolved X-ray diffraction, in isotonic Ringer solution (1T), hypertonic (1.4T) and hypotonic (0.8T) solutions. Fast stretches (0.4-0.6 ms duration and 16-25 nm per half-sarcomere (nm hs(-1)) amplitude) were applied at various tensions during the force development in isometric tetani. Force increased during the stretch up to a peak (critical tension, Pc) at which it started to fall, in spite of continued stretching. In all solutions, Pc was proportional to the initial isometric tension developed. For a given isometric tension, Pc increased with solution tonicity and occurred at a precise sarcomere elongation (critical length, Lc) which also increased with tonicity. M3 meridional layer line intensity (I M3) was measured during the application of sinusoidal length oscillations (1 kHz frequency, and about 2% fibre length amplitude) at tetanus plateau. I M3 changed during the length oscillations in a sinusoidal manner in phase opposition to length changes, but a double peak distortion occurred at the peak of the release phase. The presence of the distortion, which decreased with tonicity, allowed calculation of the mean position of the myosin head (S1) during the oscillation cycle. In agreement with the lever arm theory, both X-ray diffraction and mechanical data show that solution tonicity affects S1 mean position and consequently crossbridge individual extension and force, with no effect on crossbridge number. The force needed to break the single crossbridge was insensitive to solution tonicity suggesting a non-ionic nature of the actomyosin bond.

Position and Orientation of Phalloidin in F-Actin Determined by X-Ray Fiber Diffraction Analysis

Knowledge of the phalloidin binding position in F-actin and the relevant understanding of the mechanism of F-actin stabilization would help to define the structural characteristics of the F-actin filament. To determine the position of bound phalloidin experimentally, x-ray fiber diffraction data were obtained from well-oriented sols of F-actin and the phalloidin-F-actin complex. The differences in the layer-line intensity distributions, which were clearly observed even at low resolution (8 Å), produced well-resolved peaks corresponding to interphalloidin vectors in the cylindrically averaged difference-Patterson map, from which the radial binding position was determined to be ∼10 Å from the filament axis. Then, the azimuthal and axial positions were determined by single isomorphous replacement phasing and a cross-Patterson map in radial projection to be ∼84° and 0.5 Å relative to the actin mass center. The refined position was close to the position found by prior researchers. The position of rhodamine attached to phalloidin in the rhodamine-phalloidin-F-actin complex was also determined, in which the conjugated Leu(OH) 7 residue was found to face the outside of the filament. The position and orientation of the bound phalloidin so determined explain the increase in the interactions between long-pitch strands of F-actin and would also account for the inhibition of phosphate release, which might also contribute to the F-actin stabilization. The method of analysis developed in this study is applicable for the determination of binding positions of other drugs, such as jasplakinolide and dolastatin 11.

Direct Modeling of X-Ray Diffraction Pattern from Skeletal Muscle in Rigor

Available high-resolution structures of F-actin, myosin subfragment 1 (S1), and their complex, actin-S1, were used to calculate a 2D x-ray diffraction pattern from skeletal muscle in rigor. Actin sites occupied by myosin heads were chosen using a “principle of minimal elastic distortion energy” so that the 3D actin labeling pattern in the A-band of a sarcomere was determined by a single parameter. Computer calculations demonstrate that the total off-meridional intensity of a layer line does not depend on disorder of the filament lattice. The intensity of the first actin layer A1 line is independent of tilting of the “lever arm” region of the myosin heads. Myosin-based modulation of actin labeling pattern leads not only to the appearance of the myosin and “beating” actin-myosin layer lines in rigor diffraction patterns, but also to changes in the intensities of some actin layer lines compared to random labeling. Results of the modeling were compared to experimental data obtained from small bundles of rabbit muscle fibers. A good fit of the data was obtained without recourse to global parameter search. The approach developed here provides a background for quantitative interpretation of the x-ray diffraction data from contracting muscle and understanding structural changes underlying muscle contraction.

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

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.

The likelihood function in fiber diffraction

The likelihood function is an appropriate target function for refinement of molecular structures using fiber diffraction data. However, its practical application to fiber diffraction faces two significant obstacles: (i) the intensities of layer lines in a fiber diffraction pattern usually arise from the superposition of several terms, each equivalent to a crystallographic structure factor, thereby making the calculation significantly more complex than for the crystallographic case; (ii) to describe a molecular structure at the atomic level based on fiber diffraction data, the radial and phase parts of the atomic coordinates must be treated separately owing to the uniaxial symmetry of the structure. These issues are addressed here in order to derive equations of likelihood functions for fiber diffraction. The special case of a single term on a layer line is treated first followed by extension of the method to the multiterm case. A practical difficulty in implementation of likelihood for the multiterm case is that each term has a different variance. An analytical technique is described that allows the conversion of the unequal-variance case to an equal-variance case. This makes it possible to express the likelihood by an explicit formula, allowing a direct implementation of the likelihood calculation. A cylindrically symmetric model is proposed for error distribution of the atomic coordinates in a helical structure. Variances and offset coefficients of the contributing terms in the likelihood functions are expressed in terms of the variance of the atomic coordinates in the cylindrical reference system.

The Effect of Thin Filament Activation on the Attachment of Weak Binding Cross-Bridges: A Two-Dimensional X-Ray Diffraction Study on Single Muscle Fibers

To study possible structural changes in weak cross-bridge attachment to actin upon activation of the thin filament, two-dimensional (2D) x-ray diffraction patterns of skinned fibers from rabbit psoas muscle were recorded at low and high calcium concentration in the presence of saturating concentrations of MgATP γS, a nucleotide analog for weak binding states. We also studied 2D x-ray diffraction patterns recorded under relaxing conditions at an ionic strength above and below 50 mM, because it had been proposed from solution studies that reducing ionic strength below 50 mM also induces activation of the thin filament. For this project a novel preparation had to be established that allows recording of 2D x-ray diffraction patterns from single muscle fibers instead of natural fiber bundles. This was required to minimize substrate depletion or product accumulation within the fibers. When the calcium concentration was raised, the diffraction patterns recorded with MgATP γS revealed small changes in meridional reflections and layer line intensities that could be attributed in part to the effects of calcium binding to the thin filament (increase in I 380, decrease in first actin layer line intensity, increase in I 59) and in part to small structural changes of weakly attached cross-bridges (e.g., increase in I 143 and I 72). Calcium-induced small-scale structural rearrangements of cross-bridges weakly attached to actin in the presence of MgATP γS are consistent with our previous observation of reduced rate constants for attachment and detachment of cross-bridges with MgATP γS at high calcium. Yet, no evidence was found that weakly attached cross-bridges change their mode of attachment toward a stereospecific conformation when the actin filament is activated by adding calcium. Similarly, reducing ionic strength to less than 50 mM does not induce a transition from nonstereospecific to stereospecific attachment.

Iterative Low-Pass Filtering for Estimation of the Background in Fiber Diffraction Patterns

Disorientation of particles in fibrous specimens results in diffraction patterns in which the layer-line intensity is arced about the center, causing layer lines to overlap at larger radii and, as a consequence, making correction of the background problematic. Taking advantage of the fact that the background is typically made up of spatial frequencies that are substantially lower than those constituting the diffracted intensities, estimates of background in fiber diffraction patterns were made by applying an iterative low-pass filter to the diffraction data. This procedure has been applied to X-ray fiber diffraction patterns from filamentous bacteriophages to calculate the intensities along layer lines as well as to correct for the background.

Radial Mass Analysis of the Flagellar Filament of Salmonella: Implications for the Subunit Folding

X-ray fiber diffraction patterns of the R-type straight flagellar filament of Salmonella typhimuriumSJW1655 strain showed layer-lines with an axial spacing of 1/437 Å, which could be resolved only due to very small disorientation angles (<2 °) of the filaments in oriented sol specimens. Although the equatorial layer-line was situated between the relatively strong first layer-lines right above and below it, these small disorientation angles and a new method of two dimensional angular deconvolution allowed us to determine the equatorial layer-line intensities quite accurately. The equatorial data were phased by using the amplitude difference between the native flagellar filament and its heavy atom derivatives. One of the heavy-atom derivatives was prepared by introducing a cysteine residue by site-directed mutagenesis and applying a mercury compound. From the equatorial structure factors, the radial density distribution of the filament was calculated at 11 Å resolution. A prominent feature was two pairs of high density peaks at radii of around 25 and 45 Å and a deep density trough between them, which corresponds to the concentric double tubular structure in the core region that has been found in the density map recently deduced by helical image reconstruction from electron micrographs of frozen hydrated filaments. The molecular masses were estimated for four radial segments that correspond to the morphological domains identified in the map of helical image reconstruction. Then the domains were assigned to sequence positions by correlating the estimated masses with those of proteolytic fragments of flagellin. The assignment is consistent with the distributions of secondary structures and in particular α-helical coiled-coils that were predicted from the sequence. It also helps to understand how the polymerization behaviour is affected by truncation of the disordered terminal regions of flagellin and why mutations in a specific region are responsible for changes in the polymorphic shape of the filament.>

X-ray diffraction studies on oriented gels of vertebrate smooth muscle thin filaments

The ATPase activity of acto-myosin subfragment 1 (S1) at low ratios of S1 to actin in the presence of tropomyosin is dependent on the tropomyosin source and ionic conditions. Whereas skeletal muscle tropomyosin causes a 60% inhibitory effect at all ionic strengths, the effect of smooth muscle tropomyosin was found to be dependent on the ionic strength. At low ionic strength (20 m m) smooth muscle tropomyosin inhibits the ATPase activity by 60%, while at high ionic strength (120 m m) it potentiates the ATPase activity three-to five-fold. Therefore, the difference in the effect of smooth muscle and skeletal muscle tropomyosin on the acto-S1 ATPase activity was due to a greater fraction of the tropomyosin—actin complex being turned on in the absence of S1 with smooth muscle tropomyosin than with skeletal muscle tropomyosin. Using well-oriented gels of actin and of reconstituted specimens from vertebrate smooth muscle thin filament proteins suitable for X-ray diffraction, we localized the position of tropomyosin on actin under different levels of acto-S1 ATPase activity. By analysing the equatorial X-ray pattern of the oriented specimens in combination with solution scattering experiments, we conclude that tropomyosin is located at a binding radius of about 3.5 nm on the f-actin helix under all conditions studied. Furthermore, we find no evidence that the azimuthal position of tropomyosin is different for smooth muscle tropomyosin at various ionic strengths, or vertebrate tropomyosin, since the second actin layer-line intensity (at 17.9 nm axial and 4.3 nm radial spacing), which was shown in skeletal muscle to be a sensitive measure of this parameter, remains strong and unchanged. Differences in the ATPase activity are not necessarily correlated with different positions of tropomyosin on f-actin. The same conclusion is drawn from our observations that, although the regulatory protein caldesmon inhibits the ATPase activity in native and reconstituted vertebrate smooth muscle thin filaments at a molar ratio of actin/tropomyosin/caldesmon of 28:7:1, the second actin layer-line remains strong. Only adding caldesmon in excess reduces the intensity of the second actin layer-line, from which the binding radius of caldesmon can be estimated to be about 4 nm. The lack of predominant meridional reflections in oriented specimens, with caldesmon present, suggests that caldesmon does not project away from the thin filament as troponin molecules in vertebrate striated muscle in agreement with electron micrographs of smooth muscle thin filaments. In freshly prepared native smooth muscle thin filaments we observed a Ca 2+-sensitive reversible bundling effect. Comparison of our data with those of contracting smooth muscle suggests that bundling of thin filaments may be important in smooth muscle contraction.

Preparing well-oriented sols of straight bacterial flagellar filaments for X-ray fiber diffraction

Well-oriented sols of straight bacterial flagellar filaments have been obtained by preparing reconstituted flagellar filaments with an appropriate length distribution and choosing appropriate solvent conditions. An average filament length of 300 to 500 nm and the use of solvents with very low concentrations of salt has allowed us to prepare highly fluid sols that make flow orientation possible. X-ray fiber diffraction from these sols has shown distinct layer-line reflections to 3.5 Å resolution in the meridional direction. Layer-line intensities have been collected by the angular deconvolution method up to 5 Å resolution. The possibility of using a magnetic field to further improve the orientation has been explored and a solvent condition that makes flagellar sols sensitive to the magnetic field has been found. General applicability of the method to other systems is also discussed.

Paracrystalline structure of poly(paraphenylene vinylene)

AbstractThe previous description1 of highly oriented films of poly(p‐phenylene vinylene) is augmented by close packing energy calculations and quantitative analysis of layer line intensity profiles observed via electron diffraction. The chain axial translational disorder is of the paracrystalline type: partial registration of chains occurs within the (100) layers while the layers themselves are randomly shifted from one another along the chain direction.