MALDI-TOF MS Analysis of Peptides

MALDI-TOF MS analysis was performed by the Proteomics Service facility at the University of Oslo, Norway, as described previously [25 (link)]. Briefly, the peptides were analyzed using an ULTRAFLEX II (Bruker Daltonics, Bremen, Germany) MALDI-TOF/TOF mass spectrometer in positive ion reflector mode. 0.4 µL sample was mixed with 0.4 µL alpha-cyano-4-hydroxycinnamic acid (Bruker Daltonics) matrix solution (10 mg/mL in 0.1% trifluoroacetic acid/acetonitrile) in a 1:1 ratio and spotted onto a MALDI plate. The mass spectra were internally calculated from the raw mass spectra using the SNAP algorithm in FlexAnalysis 2.4 (Bruker Daltonics) and compared to theoretical masses.