1. Biological Chemistry, Biomedical Sciences Division, Imperial College of Science, Technology and Medicine, Sir Alexander Fleming Building, South Kensington, London SW7 2AZ, United Kingdom, Astra Zeneca Agrochemicals, Jealotts Hill Research Station, Bracknell, Berkshire RG12 6EY, United Kingdom, and Safety of Medicines, Zeneca Pharmaceuticals, Mereside, Alderley Park, Cheshire SK10 4TG, United Kingdom