1. Division of BiochemistryDepartment of ChemistryUniversity of Crete P.O. Box 2208, GR‐71003 Voutes Greece
2. Max Planck Institute for Brain Research Max‐von‐Laue‐Straße 4 D‐60438 Frankfurt am Main Germany
3. Max Planck Institute for Biophysics Max‐von‐Laue‐Straße 3 D‐60438 Frankfurt am Main Germany