1. Departments
of Molecular Genetics
and Chemistry, The University of Toronto, Toronto, Ontario M5S 1A8, Canada
2. Department of Biochemistry, The University of Toronto, Toronto, Ontario M5S 1A8,
Canada
3. Program in Molecular
Structure, Hospital for Sick Children,
555 University Avenue,
Toronto, Ontario M5G 1X8, Canada
4. Physical and Theoretical Chemistry
Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford, Oxfordshire OX1 3QZ, U.K.