SPring-8, the large synchrotron radiation facility

Date&Time: 15:00-16:00, 12 March, 2004

Speaker: Dr. David Maughan
Affiliation: Department of Molecular Physiology & Biophysics, University of Vermont, USA

Abstract
　　We conducted time-resolved x-ray diffraction experiments on dorsal longitudinal flight muscles (DLM) of adult flies during tethered flight at the BioCAT beam line at the Advanced Photon Source.
　　X-ray diffraction patterns were collected at rest and at 8 equally spaced 350micro-sec points in the ~5 ms wing beat cycle.
　　Preliminary analysis indicates that the intensity and periodicity of both 14.5 nm and 7.2 nm reflections vary cyclically in phase with the wing beat cycle. We interpret large changes (~400%) in 14.5 nm reflection intensity as substantial changes in average cross bridge ordering, in synchrony with the wing beat cycle.
　　Smaller changes (~50%) in the 7.2 nm reflection are interpreted as reflecting increased strain in the thick filament backbone as the DLM lengthen and vice versa as the DLM shorten. Reciprocal changes spot intensities on the 38.7 and 19.3 nm layer lines indicate cyclical binding and detachment to actin target zones. These results provide strong evidence for cyclical attachment and detachment of myosin heads to actin target zones and cyclical changes in conformation of cross bridges in living flies.