1. Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
2. Present address: Graduate School of Pharmaceutical Sciences, Chiba University Chiba 263-8522, Japan
3. School of Biological Sciences, Seoul National University Seoul 151-742, Korea
4. Present address: Department of Bio-production Science, Faculty of Bioresource Science, Akita Prefectural University Akita 010-0146, Japan