Selected Reaction Monitoring: A Valid Tool for Targeted Quantitation of Protein Biomarker Discovery

Mass spectrometry (MS) is an analytical technique which is used to measure sample’s molecular mass by measuring mass to charge ratio. In this method, a soft ionization technique like ESI (Electro Spray Ionization) is used to generate charge ions. Now days, this is the most popular method for protein identification and quantitation. In shotgun proteomics proteins are digested into smaller peptides followed by analysis of complex mixture of peptides on high performance liquid chromatography (HPLC) coupled with mass spectrometry. MS based proteomics approach can be designed to use either nontargeted (shotgun) or targeted (SRM) proteomics. Bottom up shotgun MS approach is commonly used in discovery proteomics. Shotgun proteomics is a powerful tool for high-throughput peptide/protein identification and relative quantification but unsuitable for absolute quantification. In contrast to this, MS based targeted proteomics is mostly used for absolute quantification of small set of protein or peptide.