1. Department of Pharmaceutical & Biological Chemistry, The School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1N 1AX, UK and Department of Medical Biochemistry & Biophysics, Karolinska Institutet, SE-17177 Stockholm, Sweden
2. Department of Medical Biochemistry & Biophysics, Karolinska Institutet, SE-17177 Stockholm, Sweden