Recon 2 identifiers. Identifier statistics for Recon 2 before and after metabolite annotations were updated with CTS. (a) Number of unique metabolites with each of the seven types of identifiers. n: names, i: InChIKeys, c: ChEBI ID, h: HMDB ID, k: KEGG CID, p: PubChem CID, l: LipidMAPS ID. (b) Number of unique metabolites with one, and up to seven, identifiers each.