SIRIUS: decomposing isotope patterns for metabolite identification

Abstract

Motivation: High-resolution mass spectrometry (MS) is among the most widely used technologies in metabolomics. Metabolites participate in almost all cellular processes, but most metabolites still remain uncharacterized. Determination of the sum formula is a crucial step in the identification of an unknown metabolite, as it reduces its possible structures to a hopefully manageable set.

Results: We present a method for determining the sum formula of a metabolite solely from its mass and the natural distribution of its isotopes. Our input is a measured isotope pattern from a high resolution mass spectrometer, and we want to find those molecules that best match this pattern. Our method is computationally efficient, and results on experimental data are very promising: for orthogonal time-of-flight mass spectrometry, we correctly identify sum formulas for >90% of the molecules, ranging in mass up to 1000 Da.

Fig. 1.

Number of decompositions over the elements CHNOPS for intervals of width 0.001 Da. Minima and maxima taken in intervals of width 1 Da. True number of decompositions in comparison with approximate (2) (approx). As is shown in the inlay, γ(m) varies with a periodic function of period ∼1 Da.

Fig. 2.

Screenshot of the SIRIUS software, available from http://bio.informatik.uni-jena.de/sirius.