The isoMETLIN Metabolite Database is a database designed for isotpe-based metabolomics. Specifically, isoMETLIN facilitates the identification of metabolites incorporating isotopic labels. isoMETLIN enables users to search all computed isotopologues (>1 million) derived from METLIN on the basis of mass-to-charge values and specified isotopes of interest, such as ¹³C or ¹⁵N. Additionally, isoMETLIN contains experimental MS/MS data on isotopomers. These data assist in localizing the position of isotopic labels within a metabolite. From these experimental MS/MS isotopomer spectra, precursor atoms are mapped to fragments. The MS/MS spectra of additional isotopomers have then been computationally generated and included within isoMETLIN. We have also implemented a spectral-mixing function in isoMETLIN. This functionality allows users to combine MS/MS spectra from various isotopomers in different ratios to obtain a theoretical MS/MS spectrum that matches the MS/MS spectrum from a biological sample.

      By searching MS and MS/MS experimental data, isoMETLIN facilitates the identification of isotopolgues as well as isotopmers from biological samples and provides a platform to drive the next generation of isotope-based metabolomic studies.