OBSERVATION OF HOLOPROTEIN MOLECULAR-IONS OF SEVERAL FERREDOXINS BY ELECTROSPRAY-IONIZATION-MASS SPECTROMETRY

Several ferredoxins containing [4Fe-4S] or [2Fe-2S] active sites have been analyzed by electrospray-ionization-mass spectrometry. For these acidic proteins, low pH conditions must be implemented in order to ensure strong signals in positive-ionization mode. Under such conditions the iron-sulfur active sites were lost in most cases. In contrast, the holoproteins were preserved under negative-ionization mode conditions: they were weakly but sufficiently ionized and information about their cofactor content could be obtained. The experimental conditions set up here should provide a useful basis for the detailed characterization of more complex iron-sulfur proteins. (C) 1995 Academic Press, Inc.