Invertebrate myosin filament: Parallel subfilament arrangement in the wall of solid filaments from the honeybee, Apis...

Transverse serial sections (100-140 nm thick) of solid myosin filaments of the honeybee, Apis mellifica, were photographed in a JEM-200 electron microscope at 200 kV. The images were digitized and computer processed by rotational filtering. 87% of the myosin filaments showed 6-fold symmetry in their power spectra, confirming the results of earlier works (Beinbrech et al., 1988, 1991). To determine if the subfilaments were arranged parallel to the filament backbone, two methods were used. First, the three images of each myosin filament in the three serial sections were superimposed. 85% of the resulting images showed a strong peak for 6-fold symmetry and the averaged images showed 6 pairs of subfilaments, which gives evidence for parallel arrangement of the subfilaments relative to the filament axis. This result was confirmed by the second method in which a 3-dimensional reconstruction was made. An average image was made from the images of the same 17 myosin filaments from each of the three sections. The data for the 3-dimensional reconstruction were collected by tracing the outlines of the structures in the three successive sections. The resulting stereo image shows a parallel arrangement of the subfilaments.