[X-ray diffraction study of the rabbit psoas muscle with extracted H-zone]

Fibre bundles of glycerinated rabbit psoas muscle about 0.5-1.0 mm thick were incubated in 5 mM tris-(hydroxymethyl)-aminomethane (Tris), pH 8.0 for 5-20 hours at 4 degrees C. This treatment leads to selective removal of some proteins in the M-bands and H-zones of sarcomeres. Effects of extraction were analyzed on the basis of electron micrographs of longitudinal sections of muscle specimens, gel electrophoresis patterns of myofibrils and of the extracts, and measurements of the creatine kinase activity of myofibrils. In the X-ray diffraction patterns of the fibre bundles subjected to prolonged extraction a drastic decrease in the intensity of "442 A" and "223 A" meridional reflections and a considerably smaller decrease in the intensity of "212 A" meridional reflections were observed. The "147 A" meridional reflection remains practically unchanged. It was concluded that: (1) The reflections "442 A" and "223 A" were contributed mainly by diffraction on the minor proteins located in the central part of the thick filaments in between the C-zones. This is contrary to the widely accepted viewpoint according to which the appearance of "442 A" reflection is caused only by the C-protein component of the thick filaments. (2) The "147 A" meridional reflection is contributed mainly by C-protein and light meromyosin of the thick filaments.