1. Johnson Research Foundation and Department of Biochemistry and BiophysicsUniversity of Pennsylvania Perelman School of MedicinePhiladelphia Pennsylvania19104‐6059
2. Department of ChemistryUniversity of Alaska AnchorageAnchorage Alaska99508
3. Department of Physiology and BiophysicsBoston University School of MedicineBoston Massachusetts02118
4. Department of ChemistryUniversity of Colorado at DenverDenver Colorado80204