1. Research Institute, Daiichi Fine Chemical Co. Ltd., 530 Chokeiji, Takaoka, Toyama 933-8511, Japan, Department of Biochemistry, Juntendo University School of Medicine, Tokyo 113-8421, Japan, and Department of Physiology and Anatomy, Tohoku Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai 981-8558, Japan