1. Department of Chemistry, Carlsberg Laboratory (T.P.F., B.S.), and
2. Department of Physiology (F.L.), Carlsberg Laboratory, Gamle Carlsberg Vej 10, DK–2500 Copenhagen Valby, Denmark; and
3. Department of Molecular Biology, University of Southern Denmark, Odense University, Campusvej 55, DK–5230 Odense M, Denmark (E.M., P.R.)