X-ray crystallography.

X-ray crystallography has been particularly important in the study of the enzyme nitrogenase, providing researchers with high-resolution structural models that have been essential to studying the enzyme's unique metal clusters and nucleotide-binding modes and protein interactions. While several important nitrogenase structures have already been determined using X-ray crystallography, the technique still holds great potential for future significant discoveries involving reaction intermediates and redox states of the enzyme's metal clusters. Thus, it is important to inform future nitrogenase researchers about the procedures for obtaining crystals of nitrogenase component proteins and their complexes and determining their structures. While nitrogenase component proteins from several bacteria have been crystallized, the majority of structures and those of highest resolution are of the nitrogenase proteins from the bacteria Azotobacter vinelandii. Therefore, the bulk of this chapter will focus on methods for crystallization and structure determination of nitrogenase component proteins from A. vinelandii.