Application of capillary electrophoresis/ electrospray ionization‐mass spectrometry to subcellular proteomics of Escherichia coli ribosomal proteins

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Abstract
We introduce capillary electrophoresis‐mass spectrometry (CE‐MS) as an efficient means for the on‐line separation and identification of protein mixtures. It was found that while CE/electrospray ionization (ESI)‐MS analysis of whole‐cell lysate was too complicated for the one‐dimensional CE‐MS analysis, the technique was useful for the analysis of protein mixtures of moderate complexity (∼50 intact proteins). CE/ESI‐MS was applied to the subcellular proteomics of ribosomal Escherichia coli. 55 out of the 56 ribosomal proteins were detected with ease by using only ∼3.4 ng of ribosomal proteins. In addition, it was found that the mass accuracy of the conventional MS (such as quadrupole ion traps) was good enough to identify many post‐translational modifications of the intact proteins by simply comparing their measured average molecular weight with the average molecular weight predicted from gene banks.