The overlap between the thin- and thick-filament reflections in the small-angle X-ray diffraction pattern from a molluscan smooth muscle

Abstract

Small-angle X-ray diffraction studies of the living anterior byssus retractor muscle (ABRM) of Mytilus edulis have been carried out using a long (2.2 m) point-focusing camera to investigate the overlap between the thin-and thick-®lament re¯ections. While the re¯ections due to the cross-bridge lattice on the thick ®laments in the resting ABRM are distant in the axial direction from the thin®lament layer lines, the paramyosin cores of the thick ®laments produce re¯ections very close to the thin-®lament re¯ections at axial spacings of 387, 59 and 51 A Ê . Using such a long camera it becomes possible to separate these re¯ections due to an improvement in the angular resolution and increase in the difference between the widths of the thin-and thick-®lament re¯ections, and it is shown that the intensities of the 387 and 59 A Ê thin-®lament layer lines gradually drop to zero close to the meridian. It becomes relatively easy to observe the thin-®lament-based X-ray pattern by use of the long camera, making it possible to show a partial resemblance of the small-angle X-ray pattern from the contracting ABRM with the pattern from the rigorized ABRM.

Invertebrate muscles: Thin and thick filament structure; molecular basis of contraction and its regulation, catch and asynchronous muscle

“…These diagrams contain information generated by all the repeating motifs in the specimen -the thin and thick filaments and their large-scale arrangement in the sarcomere-and thus contain many more than three reflections. Determining which reflections are due to which aspects of sarcomere structure can thus be difficult (e.g., Worthington, 1959;Hanson and Lowy, 1965;Tajima et al, 1999); for an exhaustive identification of the sources of all the reflections from insect flight muscle, see Reedy et al (1992). As was shown by the calculation at the end of the above paragraph, another difficulty with these data is that a given set of Xray diffraction distances are consistent with any number of heads per crown (of helices).…”

Small-angle X-ray diffraction studies of a molluscan smooth muscle in the catch state

“…In the small-angle X-ray diffraction pattern from the ABRM in the active state, weak reflections similar to the layer line reflections in the rigor pattern appeared under the 5.9 nm layer line (Fig. 10 ) (Tajima et al 1994b , 1999a ). Time-resolved small-angle X-ray diffraction showed that the rigor-like reflections increased in intensity with the increase in tension induced by stimulation with either a high (10 −3 M) or low (10 −5 M) concentration of ACh solution.…”