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.

Diffraction from insect flight muscle

Using this beam line, the Heidelberg group (in collaboration with Richard Tregear from Oxford) studied the diffraction from insect flight muscle. The excellent collimation led to detailed fibre diffraction pictures which yielded new structural information (Holmes et al ., 1980). Time resolved experiments were set up with oscillating insect flight muscle. The muscles were attached to a vibrator and oscillated at 5 Herz at which frequency they generate considerable work if provided with ATP. At low amplitudes of oscillation it was expected that the cross bridges might be partially synchronized so that one should be able to record diffraction patterns from various parts of the cross-bridge cycle. The diffraction was recorded, a layer line at a time, on a position sensitive detector and the output switched into one of 32 bins in synchrony with the oscillation. Data with usable statistics could be obtained from the equator in about 15mins. However, on account of the available intensity, the measurements remained confined to the strong equatorial reflexions (Barrington Leigh & Rosenbaum, 1976). Unfortunately, these reflexions alter little between resting and contracting insect flight muscle and, therefore, are not very useful for monitoring the cross-bridge swing. We were not observing the cross bridges in flagranti . The insect flight muscle experiments needed a storage ring!

Since the intensity was not adequate to allow a time resolved study of the meridional reflexions (which do alter with cross bridge orientation) attempts were made to "freeze" the cross-bridges in alternative conformations by the use of non-hydrolysable analogs of ATP (Goody et al ., 1976). Quite large changes in the diffraction pattern were induced by certain analogs. However, a large part of the changes resulted from alterations in the pattern of binding of the cross bridges to actin, rather than in an underlying change in the cross-bridge orientation (Goody et al ., 1975).

The group shared experiences with Hugh Huxley and Uli Arndt in Cambridge who were setting up a similar beam line at NINA for experiments on frog muscle.

Zur Redakteursansicht