1. Leiden/Amsterdam Center for Drug Research, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA, Leiden, The Netherlands, Division of Dermatology, Department of Medicine, University of British Columbia, 835 West 10th Avenue, Vancouver, British Columbia, Canada, V4Z 4E8, and Department of Physics/Institute of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada, V5A 1S6