1. Department of Physiology, Nippon Medical School, Sendagi 1-1-5, Bunkyo-ku, Tokyo 113, Japan
2. The Shiga Medical Center for Adult Disease, Moriyama, Shiga 524, Japan
3. Laboratory of Chemical Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA