The synchrotron Laue method

The original X-ray diffraction experiment was based on an idea of von Laue and conducted by Friedrich and Knipping (Friedrich et al 1912). It earned von Laue the Nobel Prize for Physics in 1914. The basis of the idea was that if X-rays were electromagnetic waves then their wavelengths might be of the same order as the interatomic separation in crystals and diffraction would be observed. The original diffraction photograph was from a crystal of copper sulphate. 

The first analyses of simple crystal structures were made using Laue photographs when W. L. Bragg deduced the structure of sodium chloride and other alkali halide crystals (for a historical review see Bragg (1975)). Subsequently, Bragg primarily used the monochromatic X-ray 

The universal spectral curve of SR, however, ideally lends itself to Laue geometry since a broad band of wavelengths of high intensity is emitted by the synchrotron electron beam. As a result, a very large number of reflections can be recorded in a remarkably short exposure time in a Laue experiment this has led to a revival of the Laue method as a means for quantitative structure analysis, especially for kinetic studies and the analysis of structural perturbations. Time resolved investigations include the study of enzyme or zeolite catalysis in crystals. The perturbations which are of interest include the effects of electric fields, pressure and temperature on various materials. 

In the monochromatic rotating crystal method it has been feasible to record complete data sets from a protein crystal on a timescale of half an hour or less using an SR source (see chapter 10). Ultimately, the total data collection time in the monochromatic method is set by the mechanical overheads of the angular rotation speed of the crystal and by the necessity to replace film cassettes or transfer detector images to computer mass store and to refresh the detector. 

This chapter concentrates on the development of the Laue method, and the way in which it is employed, at SR sources. 

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It seems that a substantial part of the radiation damage in proteins and viruses (and some other crystals, too) is a function of time from the first exposure to the beam. The synchrotron Laue method allows complete data recording in a shorter time from first exposure than any other method. Of course, protein crystals differ greatly in their susceptibility to radiation damage. For example, some survive a single exposure while, at the other extreme, cases such as pea lectin can survive many exposures. Indeed, it now seems that many protein crystals (>50%) are able to yield high quality synchrotron Laue diffraction photographs. 

A study on a low pH form of carbonic anhydrase (Lindahl et al 1990) has shown that a sensitivity to the scattering of 1 water molecule in 29 000 Da of enzyme is possible with the synchrotron Laue method (figure 7.17). 

Calcium binding to tomato bushy stunt virus has been studied using the synchrotron Laue method (Hajdu et al 1989). The non-crystallo-graphic symmetry of the virus crystal aided the clarity of the final map in showing up the calcium sites. A novel spatial deconvolution algorithm was used to obtain intensity estimates of the individual diffraction spots (Shrive, Clifton, Hajdu and Greenhough 1990). 

Application of the synchrotron Laue method to time resolved... 

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