SYNCHROTRON X-RAY CRYSTALLOGRAPHY TECHNIQUES - TIME-RESOLVED ASPECTS OF DATA-COLLECTION

Synchrotron X-radiation (SR) is intense, polychromatic and collimated. These properties are exploited routinely now to measure data at high resolution from proteins or from large unit cells (e.g. viruses), particularly using a monochromatized short wavelength beam. The time needed to measure protein crystal data-sets (in rotation geometry) can be quick (hours or minutes) compared with laboratory sources (weeks or days). Even so, more rapid data collection is of interest for time-resolved macromolecular crystallography. White beam:stationary crystal (Laue) geometry at SR sources offers shorter exposure times (seconds and less with film). Laue data-sets can be sensitive to subtle structural differences. Technical challenges still presented by SR Laue patterns include the energy overlap of low-resolution data and the spatial overlap of spots, both of which affect the completeness of data-sets. Some energy deconvolution is already possible by the use of multiple films. The spatial overlap problem can be alleviated by the use of three-dimensional detectors, such as a `toast-rack' of plates. Monitoring of a crystalline process, via the Laue pattern, requires time slicing detector systems (e.g. based on CCDs) to be developed.