A comparison of X-ray small-angle scattering results to crystal structure analysis and other physical techniques in the field of biological macromolecules

In principle, there exist two ways to contribute to structure determination of macromolecules by X-ray diffraction: ( a ) by analysing diffraction data obtained from the crystalline state, and ( b ) by interpretation of X-ray small-angle scattering from particles in solution. The brilliant achievements of X-ray crystal-structure analysis of macromolecules, initiated by the works of Perutz on heamoglobin and Kendrew on myoglobin, are well known and it is evident that its detailed elution of secondary, tertiary and quaternary structure cannot be matched by any other means. However, a number of necessary prerequisites for a successful application, as, for example, the availability of well-defined crystals and heavy atom labelled derivatives thereof to surmount the problem of phase determination are not always given.