The Possibilities of MALDI and ESI

The MALDI-TOF mass spectrometer determines the MW of the protein. Because it also analyzes protein mixtures (separates protein mixtures substantially better than SDS gel electrophoresis), it can perform many functions of SDS gel electrophoresis. For example, the MALDI-TOF provides convincing data about the purity of proteins. As far as the sensitivity is concerned, you need 10 to 100 fM less protein for the MALDI-TOF spectnun than for the silver staining of an SDS gel. However, the MALDI-TOF mass spectrometer offers more than the SDS gel electrophoresis. 

Oligosaccharides can also be incorporated into matrix crystals and gasified. Actually, you should even be able to sequence the oligosaccharides with the MALDI-TOF (ladder sequencing see Section 7.6.5 and Stahl et al. 1994). In principle, MALDI brings any polymer into the gas phase, even polyethylene glycol. However, you have to supply such neutral polymers with a positive charge. Otherwise, the electric field cannot accelerate them into the TOE These polymers are therefore complexed with metal ions (whose MW, of course, needs to be taken into account). 

The big hope of ESI is to be able to analyze noncovalent protein complexes (Loo 1997). This would allow quick and reliable examinations of the stoichiometry of the protein complexes. No more elaborate and dubious cross-linking assays (see Chapter 8), but two ESI runs—one imder native conditions—and one imder denaturing conditions—and there is your answer. 

With good instruction, you can learn within two weeks how to work with the MALDI-TOF mass spectrometer and how to crystallize. With the ESI it is even faster, because you do not have to crystallize. With most devices you get helpful analysis software. In summary a mass spectrometer is not cheap, but it is worth the expense. 

Beavis, R., and Chait, B. (1996). Matrix-assisted Laser Desorption Ionization Mass Spectrometry of Proteins, Methods Enzymol. 270 519-551. 

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