Two-dimensional mass spectrometric mapping.

The identification and relative quantification of proteins in closely related biological samples is the backbone for many investigations in systems biology and for the discovery of biomarkers. While two-dimensional gel-based methodologies are still widely used for comparative proteomic studies, the recent advent of gel-free methodologies may allow the analysis of a larger number of samples in an automated fashion. Most of the technologies presented in this review require a chemical modification of proteins before analysis, and rely on the relative intensities of mass spectrometry signals for protein quantification. In particular, two-dimensional mass spectrometric mapping methodologies provide a visual representation of mass spectrometric data, thus facilitating the identification of differences in relative protein abundance.