The entries in BTO are updated bi-annually as part of the major update of BRENDA. It is available via the BRENDA website in the category “[https://www.brenda-enzymes.org/ontology.php Ontology Explorer]”. The enzyme source terms can be searched via the BTO query form. As a result, the user receives a list of EC numbers which are directly connected to  the enzyme information of BRENDA. It is also possible to search via the BRENDA “Source Tissue” search form (“Classic View”). The result page displays all enzymes which are isolated or detected in the searched tissue term, directly linked to BTO.
BTO and BRENDA are freely accessible for academic users. It can be freely downloaded via the “[https://www.brenda-enzymes.info/ontology/tissue/tree/update/update_files/BrendaTissueOBO Ontology Explorer]” of the BRENDA website or in the OBO format from “[http://www.obofoundry.org/ontology/bto.html Obofoundry]”.