Secreted proteins found in the supernatant of different mutants were analyzed by mass spectrometry employing In source-CID. After analysis of intact N-glycopeptides on MS1 level, N-glycan compositions found were compared between two strains, consequently unraveling the molecular function of enzymes knocked down. Hereby, the role of a putative fucosyltransferase and the identity of a second core- xylosyltransferase could be confirmed.