isotopetagged

Isotopetagged refers to the use of stable isotopes to label molecules in order to distinguish and quantify samples in mass spectrometry–based analyses. The technique relies on introducing a defined mass difference between labeled and unlabeled (or differently labeled) samples, enabling their combined analysis and subsequent relative or absolute quantification.

Two main strategies are used. Metabolic labeling, such as stable isotope labeling by amino acids in cell culture (SILAC), incorporates heavy isotopes (for example 13C or 15N) into newly synthesized proteins as cells are grown in isotope-enriched media. Chemical or metabolic labeling attaches isotope-containing tags to peptides or proteins after sample preparation. Classic chemical methods include isotope-coded affinity tags (ICAT), which use light and heavy variants to label cysteine residues, and isobaric tagging approaches like iTRAQ and TMT (tandem mass tags), which label peptides with chemically identical masses but yield distinct reporter ions upon fragmentation for multiplexed quantification.

Isotopetagged workflows often enable multiplexing, allowing several samples to be analyzed in a single liquid chromatography–mass spectrometry run. This increases throughput and helps reduce technical variation, which can improve quantification accuracy in complex proteomes or metabolomes.

Applications span quantitative proteomics, including measurement of differential protein abundance, protein turnover studies, and analyses of signaling pathways or interactions. Limitations can include incomplete labeling, higher cost, and potential quantitative biases from isotopic impurities or co-eluting species. Careful experimental design and appropriate data-analysis pipelines are essential to obtain reliable results from isotopetagged experiments.