Substructures in the core of thick filaments: arrangement and number in relation to the paramyosin content of insect flight muscles.
Transverse sections (100-140 nm thick) of solid myosin filaments of the flight muscles of the honeybee, Apis mellifica, the fleshfly, Phormia terrae-novae and the waterbug, Lethocerus uhleri, were photographed in a JEM-200 electron microscope at 200 kV. The images were digitized and computer processed by rotational filtering. The power spectra of the images of each of these filaments showed six-fold symmetry for the outer wall region and three-fold symmetry for the inner wall region. Images of the honeybee additionally showed three-fold symmetry for the center of the filament. Considering both paramyosin content of the myosin filaments and the results of the rotational filtering, we suggest the existence of 3 paramyosin strands in the myosin filaments of the fleshfly, 6 paramyosin strands in the honeybee filaments and 5 strands in the myosin filaments of the waterbug. In the case of the honeybee, the 3 paramyosin strands of the inner wall are positioned directly opposite the myosin subfilaments, while the 3 strands of the center seem to be arranged opposite the gaps between the myosin subfilaments. The paramyosin filaments of the fleshfly wobble between 2 myosin subfilaments, without loosing their three-fold symmetry arrangement in the inner wall. The 3 paramyosin strands in the inner wall of the waterbug myosin filaments are either arranged opposite the myosin subfilaments or opposite the gaps between the subfilaments. Finally, we were able to generate a 3-dimensional reconstruction of the myosin filament of the honeybee, showing the parallel arrangement of both, myosin subfilaments and paramyosin strands, relative to the long filament axis.
Schmitz
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H
Duke University, Medical Center, Department of Cell Biology, Durham, NC 27710, USA.
Ashton
F T
FT
Pepe
F A
FA
Beinbrech
G
G