Biological Structural Chemistry Laboratory, Department of Chemistry, Graduate School of Science, Kyoto University Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan Tel: +81-75-753-4031 Fax: +81-75-753-4032 Graduate School of Science Bldg. No.6 Room 456 (Fukai) Room 455 (Okatsu, Takeda)