Table 5.

List of open access knowledge databases (used in the above listed web servers). Some databases have been extended into pathway browsers for interactive metabolite mapping. Although some databases are gene-centric, all of them are searchable for metabolites and represent a great source of biochemical knowledge for metabolite data interpretation.

Database	Functionalities
KEGG database and pathway browser [139]	Metabolite mapping on metabolic pathways (with annotation of the direction of changes)
Reactome database and pathway browser [140,141]	Visualization of known biological processes and pathways from intermediary metabolism, signaling, transcriptional regulation, apoptosis, disease Metabolite mapping and pathway and network visualization and analysis Pathway enrichment analysis
Cyc databases (EcoCyc, HumanCyc, MetaCyc, BioCyc) [142]	Curated database of experimentally elucidated metabolic pathways from many different model organisms Metabolite, protein, reaction, and pathway search Comparison of specific pathway and metabolic networks of different organisms
Recon database [143,144] Virtual metabolic human	Largest database of human and gut microbiome metabolism Searchable by metabolic reaction, metabolites and genes, by microorganism species, by disease, and by diet Organelle maps
WikiPathways database [145]	Pathway database maintained by scientific community Pathway browsing and editing