Department of Life Sciences, University of Tokyo^* Graduate School of Natural Science and Technology, Kanazawa University, Japan^**
○Norifumi Muraki^* Daisuke Seo^** Tomoo Shiba^* Hidehiro Sakurai^** Genji Kurisu^*

Ferredoxin-NAD(P)+ reductase (FNR) from the green sulfur bacterium Chlorobium tepidum consists of 360 residues and a flavin adenine dinucleotide. The native enzyme is dimeric with the molecular mass of 90,000Da. C. tepidum FNR sequence identifies the thioredoxin reductase-like protein but differs from the FNRs from oxygen evolving photosynthetic organisms (Seo et al., 2002). In order to determine the structure-function relationship of this interesting FNR, we have crystallized the C. tepidum FNR by hanging drop vapor diffusion method at 293 K (Figure) and crystallographically characterized the FNR crystals. Diffraction data to 2.4 Å resolution were collected using synchrotron radiation. The crystals belong to the space group of C222₁. Assuming two molecules in the asymmetric unit, the Matthews coefficient (V_M) was calculated to be 2.6 ų/Da, corresponding to a solvent content of 53.2 %. Non-crystallographic symmetry (NCS) of crystals was explored with self-rotation functions using the program POLARFN in the CCP4 program suite, giving no significant peaks. The NCS peaks might overlap the peaks from crystallographic symmetry. The structure determination using heavy atom derivatives is now in progress.