1. Department of BiochemistryUniversity of Stockholm, Arrhenius Laboratories A4 S‐106 91 Stockholm Sweden
2. Department of Medical Biochemistry & BiophysicsKarolinska Institutet S‐171 77 Stockholm Sweden
3. Department of Chemistry and The Skaggs Institute for Chemical BiologyThe Scripps Research Institute 10550 North Torrey Pines Rd. La Jolla California 92037 USA