Mapping O‐glycosylation of apolipoprotein C‐III in MALDI‐FT‐ICR protein profiles

Ultrahigh resolution MALDI ‐ FT ‐ ICR profiles were obtained from human serum samples that were processed using a fully automated RPC 18‐based magnetic bead method. Proteins were profiled from m/z value 6630 with a resolving power of 73 000 up to m/z value 12 600 with a resolving power of 37 000. In this study, a detailed evaluation was performed of the isoforms of apolipoprotein C‐III, i.e. the different mucin‐type core 1 O ‐glycans with the addition of one or two sialic acid residues. The MALDI ‐ FT‐ICR profiles are discussed with regard to reproducibility of the signal intensities as well as the accurate mass measurements. ESI ‐ FT‐ICR ‐ MS / MS analyses of the same serum samples were performed to confirm the identity of apolipoprotein C ‐III glycoforms.