1. Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
2. Forefront Research Center, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
3. Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita 565-0871, Japan