Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry of multimeric metalloproteins

Five multimeric metalloprotein species are examined by electrospray ionizat ion Fourier transform ion cyclotron resonance mass spectrometry. Isotopical ly resolved mass spectra are obtained for noncovalent complexes with masses ranging from 25 to 86 kDa. Samples must be rigorously desalted, as these l arge molecules offer more sites for proton-sodium exchange, and the heterog eneity of multiply sodiated species causes a decrease in the duration of th e beat signal in the acquired transient, and thus a decrease in signal to n oise. Desalting methods reported by others for multimeric proteins, for exa mple buffer exchange with citrate, cause loss of the metal center in the pr oteins studied here. Extensive dialysis was found to be necessary in order to observe isotopically resolved mass spectra. With these methods. multimer ic complexes are observed for iron-sulfur proteins as well as heme proteins . (C) 2001 Elsevier Science B.V.