Analysis of phospho- and glycopolypeptides with infrared matrix-assisted laser desorption and ionization

The analytical characteristics of infrared (IR) matrix-assisted laser desor ption and ionization (MALDI) were investigated for the analysis of phosphop eptides, a phosphopolypeptide, and glycopeptides. Two commercially availabl e instruments, a high-resolution delayed extraction (DE) reflectron time-of -flight (RETOF) mass spectrometer and a high-power pulsed Er:YAG laser, wer e interfaced to produce a high-resolution MALDI-DE-RETOF instrument that is easy to use and can be switched between Wand IR-MALDI mode within seconds. In the interface design, particular attention was paid to maintaining the same professional operating environment for the new IR-MALDI mode as exists for the commercial UV-MALDI mode. This instrument configuration facilitate s comparative observation and investigation of the relative analytical meri ts of IR- and UV-MALDI. The results of studies of the tryptic a-casein phos phopeptides, RP1 (a Thr(45)-monophosphorylated congener of the recombinant protein hirudin variant 1), and fetuin Asn(81) tryptic glycopeptides are pr esented. The elimination of labile substituents such as phosphoric acid and sialic acid is suppressed in IR-MALDI-RETOF mass spectrometry, with concom itant higher analyte ion yields. These results reflect the advantages that accrue from deposition of significantly less internal energy in the case of IR-MALDI.