Polypeptide fingerprinting methods, metabolic profiling, and bioinformatics database

A method for analyzing a metabolic pathway, comprising (a) administering to a subject a known ratio of a labeled substrate and an unlabeled substrate, wherein said labeled substrate labeled with a stable isotope and said unlabeled substrate having a natural abundance of said stable isotope; (b) allowing the labeled substrate and the unlabeled substrate to be at least partially metabolized to form a labeled target metabolite and an unlabeled target metabolite; (c) generating mass spectral data from a plurality of samples from said subject at a plurality of time points; and (d) determining a plurality of relative abundances of said labeled target metabolite to said unlabeled target metabolite from the mass spectral data of at least one of said samples and comparing said plurality of relative abundances to said known ratio of said labeled substrate and said unlabeled substrate.