Figure 5
(a) Arrangement of myosin crossbridge and C-protein molecules on the thick filament (1.6 µm long) in the relaxed frog muscle derived from the analysis of meridional X-ray patterns. In each crossbridge zone there are perturbed regions with an axial period of 42.9 nm (red) in which C-protein binding regions sit (green). Regular regions exist with a separation of 14.3 nm at either distal end (yellow). (b) The axially projected density model of the thick filament in the crossbridge perturbed region is shown on the right-hand side. Each square bar corresponds to the mass density of one crossbridge projecting level projected onto the fibre axis. The axial distance between projection levels in a triplet was ∼12.6 nm. The hatched area denotes the C-protein density. On the left-hand side is shown the resting arrangement of two headed myosin crossbridges expected from the model shown on the right (where C-protein molecules are deleted) in which each head structure was modelled from the crystal structure (Rayment et al., 1993). |