Alterations of crossbridge angle induced by beta, gamma-imido-adenosine-triphosphate. Electron microscope and optical diffraction studies on myofibrillar fragments of abdominal muscles of the crayfish Orconectes limosus.

The molecular basis of muscle contraction is thought to consist of cyclic movements of parts of the myosin molecules (crossbridges). Unitl now different states of the proposed crossbridge cycle could be stablilized and demonstrated by electron microscopy only in the case of highly specialized insect flight muscles. In this paper evidence is presented that it is also possible to induce crossbridge positions corresponding to the rigor [16] and the pseudorelaxed state [3] in non-insect muscles. Homogenization of myofibrils of the abdominal flexors of the crayfish Orconectes limosus in rigor or AMP.PNP-containing solutions brings about two different crossbridge patterns: The formation of crossbridges attached to the actin filaments in a mainly acute (rigor) or in a mainly perpendicular angle (pseudo-relaxed). Optical diffraction patterns taken from electron micrographs of sarcomere fragments are likewise compatible with those taken from sarcomeres of insect flight muscles fixed in comparable conditions [2,3].