[X-ray study of the effect of pyrophosphate on thick filament structure in skinned fiber bundles of the rabbit psoas muscle].

Structure of thick filaments in the chemically skinned fibre bundles of rabbit psoas muscle in a state of pseudorelaxation induced by adding 2 mM pyrophosphate (PP) and of PP-mixture with 40% ethyleneglycol to the bathing rigor solution was studied with the help of X-ray diffraction technique. Reduction in the isometric rigor tension by about 50-70% in a state of pseudorelaxation is accompanied by significant changes in the relative intensities of a number of meridional reflections, indicating that in situ the structure and location of S-2 segment may be regulated by the structural changes in the acto S-1-complex during its cyclic interaction with ATP.