1. Department of Medicine, University of Sheffield Clinical Sciences Center, Northern General Hospital (R.S.M., M.S.A., E.H.K., P.F.W., A.P.W.), Sheffield, United Kingdom S5 7AU;
2. the Department of Biochemistry, Medical Center of Postgraduate Education (A.G.), Warsaw 01 813, Poland;
3. the Department of Medicine, Kings College School of Medicine (J.P.B.), Denmark Hill, London, United Kingdom SE5 8RX