Analysis of glycated proteins by mass spectrometric techniques: qualitative and quantitative aspects.

The analysis of protein glycation poses a difficult challenge due to the complex nature of the reaction. Of the several methods developed for the qualitative and quantitative evaluation of the glycation reaction between proteins and reducing sugars, soft ionization mass spectrometry is the most direct and reliable. In this paper we review the major mass spectrometric methods (ESI and MALDI mass spectrometry) used in the study of protein glycation. We also tested the assumption that limited glycation has little or no effect on the ionization potential of proteins and that the distribution profile of molecular ion peaks of different glycoforms in a mass spectrum reflect their solution composition in a mixture. The results confirm the validity of the above assumption under dilute solution conditions (0.2-0.6 g/ml total protein). A comparison of ESI and MALDI mass spectrometry in the analysis of protein glycation showed that both methods provide qualitative and quantitative analytical results, but the choice of instrument depends on the nature of the sample to be analysed, the level of accuracy and the type of information that is required.