HIGH-RESOLUTION X-RAY-DIFFRACTION OF MUSCLE USING UNDULATOR RADIATIONFROM THE TRISTAN MAIN RING AT KEK

High-resolution X-ray diffraction studies on striated muscle fibres we re performed using a hard Xray undulator installed in the Tristan main ring at KEK, Tsukuba, Japan. The performance of the undulator, along with an example experiment which exploited the unique characteristics of undulator radiation, are reported. The vertical divergence angle of the first harmonic of the undulator was similar to 10 mu rad under 8 GeV multi-bunch operating conditions and the peak photon flux density was estimated to be similar to 3 x 10(16) photons s(-1) mrad(-2) (0.1% bandwidth)(-1) (10 mA)(-1). The well collimated X-ray beam from the u ndulator made it possible to resolve clearly, with high angular resolu tion (similar to 700 nm), the closely spaced diffraction peaks on the meridional axis in the X-ray patterns arising from the thick filaments of a striated muscle under static conditions. By fitting the meridion al intensity pattern, a model for the molecular arrangement of the con stituent proteins in the thick filaments is proposed. These studies of muscle demonstrate the promise of undulator radiation from third-gene ration sources for high-resolution diffraction studies.