1. The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K., and Centre for Metalloprotein Spectroscopy and Biology, School of Biological Science, University of East Anglia, Norwich NR4 7RU, U.K.