Protein Standard Absolute Quantification (PSAQ) is the most advanced and reliable absolute quantification technique. The method is well-adapted for the quantification of proteins in complex matrices or for samples that undergo multiple fractionation steps before analysis. Indeed, unlike AQUA and QconCAT methods, that respectively require the use of peptides and chimeric proteins as labeled internal standards for MS-based absolute quantification, PSAQ is based on the use of full-length labeled proteins as isotope-dilution standard.

In the PSAQ technique, a cloned labeled version of the targeted protein is introduced into the sample at an early stage of the analytical process. Because the targeted and labeled proteins share identical primary structures, heterogeneities in digestion and fractionation products typically encountered with protein AQUA or QconCAT methods can be dramatically reduced.

Labeled proteins samples employed in the PSAQ strategy can be produced by employing protein expression in bacteria, insect cells or cell-free systems.

PSAQ workflow

Cortec Isotope is pleased to offer a wide range of labeled amino acids and labeled kits for protein expression.

Cortec Isotope proposes to help you label your protein. For inquiry, please contact our labeled protein expression platform.