1. Departments of Chemistry and Earth & Ocean Sciences, University of British Columbia, Vancouver, B. C., Canada V6T 1Z1, Canadian Institutes of Health Research, Group in Protein Structure and Function, Department of Biochemistry, Faculty of Medicine, University of Alberta, Edmonton, Alta, Canada T6G 2H7, Institute for Systematics and Ecology, University of Amsterdam, 1090 GT Amsterdam, The Netherlands, and Discipline of Pharmacology, University of Papua New Guinea, N.C.D., Papua New Guinea