Direct sequence analysis of proteins by in-source fragmentation during delayed ion extraction.

Continuous segments of amino acid sequence information as long as 41 residues have been deduced by interpretation of matrix-assisted laser desorption/ionization-generated ion signals dominated by Cn fragmentation within the ion source of a linear time-of-flight mass spectrometer utilizing delayed ion extraction. The technique has been applied successively to five proteins of mass 12.2 kDa to 18.3 kDa, yielding segments of continuous sequence as long as 41 residues without the need for prior proteolytic fragmentation. Intact crosslinks such as disulfides or heme linkages interrupt the generation of these data.