A high-performance neutron diffractometer for biological crystallography (BIX-3)

A high-performance neutron diffractometer for biological crystallography (BIX-3) has been constructed at JRR-3M in the Japan Atomic Energy Research Institute (JAERI) in order to determine the hydrogen-atom positions in biological macromolecules. It uses several recent technical innovations, such as a neutron imaging plate and an elastically bent silicon monochromator developed by the authors. These have made it possible to realise a compact vertical arrangement of the diffractometer. Diffraction data have been collected from the proteins rubredoxin and myoglobin in about one month, to a resolution of 1.5 Å. The data were good enough to identify the hydrogen atoms with high accuracy. By adopting a crystal-step scan method for measuring Bragg diffraction intensities, the signal-to-noise ratio was much better than that of the Laue method. This shows that BIX-3 is one of the best-performing machines for neutron protein crystallography in the world today.