1. Protein Research Unit, Princeton Biochemicals, Inc., Princeton, NJ 08540
2. Current address: Roche Diagnostic Systems, Inc., 340 Kingsland Street, Nutley, NJ 07110-1199
3. Department of Physiology, School of Medicine, Los Andes University, Merida, Venezuela
4. Department of Industrial Chemistry, Faculty of Engineering, Kyoto University, Kyoto, Japan