1. Contribution from the Noguchi Institute, 1-8-1, Kaga, Itabashi-ku, Tokyo 173-0003, Japan, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan, and Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan