1. Graduate School of Pharmaceutical Sciences, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan, Marine Biosystems Research Center, Chiba University, Amatsu-Kominato, Chiba 299-5502, Japan, and The Kitasato Institute, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8642, Japan