How x-ray diffraction with synchrotron radiation got started
The need to record low angle scattering x-ray fibre diagrams from muscle with milli-second time resolution drove the use of synchrotron radiation as an x-ray light source. The first smudgy diffraction patterns were obtained from a slice of insect flight muscle. Out of this grew the EMBL Outstation at DESY.
Time resolved studies on frog muscle
HE Huxley continued with frog muscle and transferred his work to the EMBL Outstation when this became operative (Huxley et al ., 1980). The key experiments were carried out a little later (Huxley et al ., 1981) by a team which included a number of people who have subsequently played an important role in the development of synchrotron radiation as an x-ray light source. These experiments finally showed the anticipated changes in intensity of the meridional reflexions: if a contracting muscle is released the intensity of the 14.35nm meridional reflexion drops within a few ms to a fraction of its initial value. If the muscle is extended quickly, the intensity is recovered. If one waits at the new length the intensity recovers. These experiments have recently been repeated with very high time resolution using sophisticated mechanics and the excellent two dimensional detectors at Daresbury (Irving et al ., 1992). These observations are fully consistent with the swinging cross bridge hypothesis and for many years represented the most important time resolved experiments supporting the swinging cross-bridge hypothesis.
Unfortunately, the resolution of these changes is actually too low to show the detailed molecular basis of the cross-bridge swing. Over the years it became likely that the swinging cross bridge was actually a swinging lever arm (Fig 6) (Cooke, 1986). Protein crystallography, which in turn needed synchrotron light, finally yielded insight into this mechanism.