Application of synchrotron radiation and neutrons to structure analysis for biology. Complimentary utilization

Establishment of three-dimensional crystal structures of protein was introduced, and the correlation between fundamental crystal structures and functions of protein was reviewed. The study of crystal structures of protein proceeded to following three steps; (1) preparation of protein crystals, (2) measurements by x-ray and neutron diffraction, and (3) modeling of crystal structures from mapping of electron density calculated from diffraction data. Synchrotron radiation enable us to measure x-ray diffraction with quite small crystals as small as 0.01 x 0.01 x 0.01 mm3. In order to mapping electron density, both information of a structure factor and a phase factor were required. A phase factor was determined from measurements of a specimen doped with heavy elements or anomalous dispersion from selenium replacing a part of amino acid. The results of structure analyses for flavin mononucleotide (FMN) and proteasome of cattle's lever were shown in figures. Application of neutron diffraction to structure analysis for protein was few, but if the movement of protons can be informed by neutron diffraction through measurements of water or hydrogen molecules, complementary data to the information observed by synchrotron radiation will be provided. (Y. Kazumata)