Ray Interference Measurements and Their Implications

The origin of these closely spaced peaks was very quickly shown to be the interference effects observed within the sarcomere because, in the case of C-protein, the diffraction patterns from the two C-zones in a single A-band would interfere, and, in the case of troponin, the diffraction patterns from the two troponin arrays across the Z-band would interfere. Also, in the case of the M3 multiple, the diffraction from the myosin heads in the two bridge regions of a single A-band would interfere (see summary in Squire, 1981 pages 576-582). In the case of the C-zone interference, illustrated in Fig. 21A—C), the diffraction intensity profile from a single C-zone (A) would have a prominent peak at 430 A, but the two C-zones in one A-band would be centered a distance L apart (Fig. 21C). The two C-zones could then be considered as 

Much of the recent work on interference measurements has been specifically aimed at probing crossbridge activity for this reason the main targets for study have been the M3 and M6 meridional peaks. Looking 

A-band, the interference function L would gradually increase to LN = L + 145.7 N for N crown pairs lost from overlap. 

Several groups have studied the effects on the muscle low-angle diffraction pattern of applying various mechanical perturbations to steady-state structures, either isometric contractions or rigor muscle at various strain levels. Huxley et al. (1981, 1983) used whole frog muscles and followed the effects of step changes of length of various amplitudes applied at the plateau of an otherwise isometric tetanus. They studied the effects on the M3 intensity as a whole. More recendy, with the two components of the active M3 resolved, Huxley et al. (2003) and Reconditi et al. (2003) have studied the separate behavior of these components. Huxley et al. (2003) found that the intensity ratio of the M30 to M3 varied from an initial value 

Note that the response of the M6 reflection is very different to that of the M3. It has been concluded, quite reasonably, by Huxley et al. (2003) and by Linari et al. (2000) that most of the M6 intensity must come from densities other than the myosin heads, perhaps the myosin filament 

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