from all taxonomic groups. An important part of BRENDA represent the almost 260,000 enzyme ligands, which are available on their names, synonyms or via the chemical structure. The term "ligand" is used in this context to all low molecular weight compounds which interact with enzymes. These include not only metabolites of primary metabolism, co-substrates or cofactors but also enzyme inhibitors or metal ions. The origin of these molecules ranges from naturally occurring antibiotics to synthetic compounds that have been synthesized for the development of drugs or pesticides. Furthermore, cross-references to external information resources such as sequence and 3D-structure databases, as well as biomedical ontologies, are provided. Extensions: Since 2006, the data in BRENDA is supplemented with information extracted from the scientific literature by a co-occurrence based text mining approach. For this purpose, four text-mining repositories FRENDA (Full Reference ENzyme DAta), AMENDA (Automatic Mining of ENzyme DAta), DRENDA (Disease-Related ENzyme information DAtabase) and KENDA (Kinetic ENzyme DAta) were introduced. These text-mining results were derived from the titles and abstracts of all articles in the literature database PubMed. Data access: There are several tools to obtain access to the data in BRENDA. Some of them are listed here. Several different query forms (e.g., quick and advanced search) EC tree browser Taxonomy tree browser Ontologies for different biological domains (e.g., BRENDA tissue ontology, Gene Ontology) Thesaurus for ligand names Chemical substructure search engine for ligand structures BRENDA Pathway Maps Download options: SOAP-API SBML-download BRENDA download (textfile oder JSON-Format]) Availability The use of BRENDA is free of charge. BRENDA is subject to the terms of the Creative Commons license (CC BY 4.0). Other databases BRENDA provides links to several other databases with a different focus on the enzyme, e.g., metabolic function or enzyme structure. Other links lead to ontological information on the corresponding gene of the enzyme in question. Links to the literature are established with PubMed. BRENDA links to some further databases and repositories such as: BRENDA tissue ontology ExPASy NCBI databases (Protein, nucleotide, structure, genome, OMIM, Domains IUBMB enzyme nomenclature KEGG PDB database (3D information) PROSITE SCOP CATH InterPro ChEBI Uniprot References Further reading External links Official BRENDA website Enzyme Nomenclature Springer Handbook of Enzymes Worthington Enzyme Manual ExplorEnz The Enzyme Database Enzyme databases