Troponin diffraction pattern

The diffraction pattern from troponin is very different. Here, there is one troponin complex for each tropomyosin molecule, but the end-to-end repeat along the tropomyosin strands is about 385 A It is longer than the actin filament crossover repeat of just over 357 A in vertebrate muscles (Fig. 11A and B). Because much of the troponin complex is globular, unlike tropomyosin, it shows very marked discontinuous density every 385 A along each strand of the actin filament, with the troponins in opposite strands axially shifted by the actin monomer subunit translation h of... 

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... 

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