1. Michael Barber Centre for Mass Spectrometry, Manchester Institute of Biotechnology, School of Chemistry, University of Manchester, 131 Princess Street, Manchester M1 7DN, U.K.
2. Protein Function Group, Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, U.K.
3. School of Chemistry and Chemical Engineering, Queen's University Belfast, Stranmills Road, Belfast BT9 5AG, Northern Ireland, U.K.