Absolute Quantification is a targeted quantitative proteomics technique that exhibits robust efficacy and is being increasingly utilized for a wide variety of quantitative proteomics studies. AQUA strategy is for the absolute quantification (AQUA) of proteins and their modification states. Peptides are synthesized with incorporated stable isotopes as ideal internal standards to mimic native peptides formed by proteolysis. These synthetic peptides can also be prepared with covalent modifications (e.g., phosphorylation, methylation, acetylation, etc.) that are chemically identical to naturally occurring posttranslational modifications. Such AQUA internal standard peptides are then used to precisely and quantitatively measure the absolute levels of proteins and post-translationally modified proteins after proteolysis by using a selected reaction monitoring analysis in a tandem mass spectrometer.

Advances in biological mass spectrometry have resulted in the development of numerous strategies for the large-scale quantification of protein expression levels within cells. Besides the measurements of protein expression accomplished through differential incorporation of stable isotopes into cellular proteins, the absolute quantification is a useful method in proteomics analysis.

The absolute quantification strategy: a general procedure for the quantification of proteins and post-translational modification. AQUA provides absolute quantification by employing synthetic peptides containing stable isotopes.

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