MASS AND CHARGE-STATE ASSIGNMENT FOR PROTEINS AND PEPTIDE MIXTURES VIA NONCOVALENT ADDUCTION IN ELECTROSPRAY MASS-SPECTROMETRY

A method has been developed that takes advantage of the formation of n oncovalent compounds in electrospray mass spectrometry. Mixtures of pr oteins and peptides are shown to produce an intense ion that correspon ds to a 1:1 complex with a crown ether (18-crown-6). Although the crow n ether may be added directly to the solution, for the current experim ents it is introduced via the methanol liquid sheath. The spacing of t hese complexed species in the mass spectrum allows unambiguous determi nation of the charge state of the ions and their actual mass. Through constant neutral loss scans, charge state may be determined, mass assi gned, spectra simplified, and chemical noise may be reduced for the an alysis of complex peptide samples without chromatographic separation. Finally, the prevalence of single complexation permits mass assignment s based on the mass difference of a single protein ion and its complex ed form at any charge state. Ln essence, the method performs a separat ion based on charge state. It can be used to complement chromatographi c separation and deconvolution algorithms for the electrospray mass sp ectrometry analysis of peptide-protein mixtures.