In the quantitative proteomics research, several MS-based methodologies for relative quantification have been introduced for comparison of different proteomes from collected biological samples. Meanwhile, MS-based methods for absolute quantification of specific proteins, have been developed to accurately determine the protein concentrations. According to the guidelines for bioanalytical methods, the establishment and validation of accurate analytic proposals require standard compounds of high purity for calibrating and quality controls. Currently the dominant quantitative strategy is usually a combination of shotgun method and isotope dilution strategy. The targeted proteins in the complicated biological samples would release free peptide fragments induced by specific enzymatic cleavage, and the stable peptides with unique primary sequences in the digest mixture would be utilized as surrogates for corresponding parent proteins, so the small-molecular peptides can be quantified to estimate the protein concentration.
Regarding its success in MS-based quantification of small molecules, the isotope dilution strategy has been recognized as the reference method for internal standardization, introduced into protein quantification with unique advantages over conventional ligand binding assay. In these approaches, the sample is spiked with defined amounts of stable isotope-labeled analogue(s) of unique peptides (AQUA strategy) or intact target protein(s) (PSAQ strategy), to establish the calibrating curves. The mass spec standards of high purity, no matter AQUA peptides or PSAQproteins, Creative Proteomics can help to synthesize it, to promote your research.
If the target proteins are endogenous ones for the organism and it’s not easy to obtain the blank matrix to prepare calibrating samples, only stable isotope labeled peptides or proteins, especially at the backbone of arginine and lysine, work well in the absolute quantitative proteomics. If the targeted proteins are exogenous for the organism, such as protein therapeutics, and collected blank matrix is available, naive peptides/proteins of high purity can be also used for reference standards without any isotope labeling. For both labeled and non-labeled forms, the experienced professionals can provide solid phase peptide synthesis service for peptides, and intact proteins by proper biosynthesis, folding and modifications with host cells. For SIL peptides/proteins, the products from Creative Proteomics are not only highly pure, but also offer custom peptide synthesis services with high isotope incorporation, for excellent MS analysis.
More: http://www.creative-proteomics.com/services/customized-synthesized-peptide-proteins.htm
