1. A. N. Belozersky Institute of Physico-Chemical Biology and School of Chemistry, Moscow State University, Moscow 119899, Russia, Division of Cell Biology, Linköping University, SE-581 85 Linköping, Sweden, Department of Biochemistry, University of Turku, FIN-20014 Turku, Finland, and Institute of Biotechnology, University of Helsinki, P.O. Box 56, FIN-00014 Helsinki, Finland