Fragment ion patchwork quantification for measuring site-specific acetylation degrees.

We introduce fragment ion patchwork quantification as a new mass spectrometry-based approach for the highly accurate quantification of site-specific acetylation degrees. This method combines (13)C1-acetyl derivatization on the protein level, proteolysis by low-specificity proteases and quantification on the fragment ion level. Acetylation degrees are determined from the isotope patterns of acetylated b and y ions. We show that this approach allows to determine site-specific acetylation degrees of all lysine residues for all core histones of Trypanosoma brucei. In addition, we demonstrate how this approach can be used to identify substrate sites of histone acetyltransferases.