SILu™Prot Accurate Internal Standards in Quantitative MS

By: Nadav Askari, Efrat Reem, Rotem Shaulitch, Yana Mogilianski, Tatiana Bober, Leonora Niv, Bela Lisak, Dept. of Human Protein Biology, Sigma-Aldrich Israel, Sigma-Aldrich International GmbH is a subsidiary of Merck


  • We recently developed a novel collection of Stable Isotope-labeled (SIL) full length proteins designed to be used as mass spectrometry internal standards for quantitative proteomics.
  • These standards are spiked at the initial stage of the analytical workflow, thus significantly minimizing variations.
  • Clinically-relevant SIL proteins expressed in mammalian cells have been developed.

High Purity

SILu™Prot standards are recombinant human full length SIL proteins, expressed in human cells so they are authentically folded and possess accurate PTMs. Purified by a series of chromatographic purification stages, all SILu™Prot standards are ≥95% pure by SDS-PAGE.

Best Labeling

Each SILu™Prot standard is tested for the rate of stable isotope labeling, to ensure that a heavy amino acid incorporation level of ≥98% is achieved. This test is performed for 2 or more peptides, for each lot, ensuring the lowest non-labeled impurity.

Simple workflow

The SILu™Prot standards are spiked in the beginning of the sample prep workflow, thus compensating for any errors that might have occurred during the digestion process.

Accurate results

The SILu™Prot standards showed excellent behaviour in a calibration curve. A calibration curve of MAPK3 was generated using two peptides, at a range of 0.04-0.91 μg, using SILu™Prot MAPK3 as an internal standard.

Spiked recombinant human MAPK3 was calculated in serum using the calibration curve for both peptides “NYLQSLPSK” and “ELIFQETAR, with a relative error of only 11% and 13%, respectively.

SILu™Prot collection

A wide collection of SILu™Prot standards is available, based on involvement in diseases such as:

  • Kidney Toxicity
  • Cardiovascular diseases
  • Cancer and inflammation

For more information, see