Mass spectrometric mapping and sequencing of N-linked oligosaccharides derived from submicrogram amounts of glycoproteins.

Very small quantities of glycoproteins were directly processed on a MALDI sampling plate prior to their mass spectrometric investigations. The on-plate digestion with N-glycanase released effectively the corresponding oligosaccharides in very short times, irrespective of their molecular mass. The following treatment with an array of exoglycosidase enzymes enables sequencing and a linkage-form determination in analysis times that are considerably shorter than achieved previously: the entire structural determination on a glycoprotein can be completed in one day, with a minimum substrate consumption. Ribonuclease B, bovine fetuin, human alpha 1-acid glycoprotein, and the diamine oxidase (from porcine kidney) have been used to illustrate different aspects of the on-plate sample treatment/MALDI mass spectrometry.