1. Department of Chemistry, Carlsberg Laboratory, Gamle Carlsberg Vej 10, DK-2500 Copenhagen Valby, Denmark, Biochemistry and Nutrition Group, BioCentrum-DTU, Technical University of Denmark, Søltofts Plads, Building 224, DK-2800 Kgs. Lyngby, Denmark, Institute of Food Research, Norwich Research Park, Colney, Norwich, NR4 7UA, England, and Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark