[1] Univ Leeds, Fac Biol Sci, Sch Biomed Sci, Leeds LS2 9JT, W Yorkshire, England
[2] MRC, Mol Biol Lab, Cambridge CB2 0QH, England
[3] Univ Osnabruck, Fachbereich Biol Chem, Abt Tierphysiol, D-49069 Osnabruck, Germany
[4] Univ Leeds, Fac Biol Sci, Sch Mol & Cellular Biol, Leeds LS2 9JT, W Yorkshire, England