“…Here we describe the introduction of Rhea as the reference vocabulary for enzyme annotation in UniProtKB. This development will significantly increase the utility of UniProtKB for applications such as the integrative analysis of metabolomics and other 'omics data (Kale, et al, 2016;Sud, et al, 2016), as illustrated here, as well as the study of enzyme chemistry and evolution (Rahman, et al, 2016;Tyzack, et al, 2019), the construction and annotation of metabolic models (Cottret, et al, 2018;King, et al, 2016;Moretti, et al, 2016), and the engineering of pathways for biosynthesis and bioremediation (Duigou, et al, 2019). Rhea will also provide a basis to further improve links with other knowledge resources, such as the Gene Ontology (The Gene Ontology Consortium, 2019) and Reactome (Fabregat, et al, 2018), which both plan to use Rhea as the reference for reaction chemistry (Chris Mungall and Peter D'Eustachio, personal communication).…”