Matrix-assisted laser desorption ionization (MALDI) mass spectrometry: a novel analytical tool in molecular biology...

Matrix-assisted laser desorption ionization (MALDI) is a rather recent 'soft ionization' technique which produces quasimolecular ions of large organic molecules of up to several 100 kDa molecular mass. In combination with time-of-flight (TOF) mass spectrometry it has rapidly evolved as a valuable tool for the detection and characterization of biopolymers such as peptides, proteins, oligosaccharides and -nucleotides especially in mixtures and crude samples. MALDI-MS is remarkably tolerant towards common contaminants such as salts and buffers, requires sample loads in the subpicomolar range and features a mass accuracy (and precision) of 0.1-0.01%. Structural information on analyte molecules can be obtained by exploiting metastable post source decay (PSD) processes which allow extraction of sequence or substituent information on individual peptides contained, e.g., in an enzymatic digest. Thus, MALDI provides for an easy and straight forward elucidation of posttranslational modifications. The forseeable merging of MALDI with blotting and in situ degradation techniques give MALDI-MS a key role in future laboratory practice of biotechnology and molecular biology. The actual state-of-the-art is described, and selected examples are given with special emphasis on the aspects of analytical routine work.