Gold/Fab immuno electron microscopy localization of troponin H and troponin T in Lethocerus flight muscle.

The position of the large troponin complex relative to myosin crossbridges in Lethocerus flight muscle (IFM) has been probed by electron microscopy (EM) using monoclonal antibodies against troponin T (TnT) and troponin H (TnH), a heavy troponin component found in several insect muscles. Infiltration of gold-tagged and plain Fab fragments into glycerinated IFM before fixation established in non-overlap fibers that the beads every 38.7 nm along thin filaments are troponin. Original and optically filtered EM images from 25 nm longitudinal and 15 nm cross-sections of partially overlapped fibers suggests that epitopes on both TnT and TnH are very close to the rear crossbridge of the rigor double chevron. When Fab was infiltrated into relaxed fibers and ATP was subsequently removed, the resulting rigor crossbridge lattice was disrupted by antibody labeling of the troponin. The results confirm that the lattice of rigor crossbridges and troponin are congruent and suggest that crossbridges may interact with troponin in IFM, possibly serving as a partial basis for the stretch activation characteristic of this muscle.