Rhea uses the ChEBI ontology to establish a reaction classification. ChEBI organizes chemical entities in a hierarchical fashion, where entities with a fully defined structure are subclasses of entities with a partially defined structure. When two Rhea reactions have reaction participants that are identical and/or related directly or indirectly via is a relationships in the ChEBI ontology, a Rhea curator can link them with an is a relationship to classify the more specific reaction as a subclass of the more generic reaction.

Example:

Reaction ID	Reaction equation
RHEA:22688	D-alanine + H2O + O2 = H2O2 + NH4(+) + pyruvate
RHEA:21816	a D-alpha-amino acid + H2O + O2 = a 2-oxocarboxylate + H2O2 + NH4(+)

The reaction RHEA:22688 has two participants that are specific forms of the participants of the reaction RHEA:21816:

• D-alanine (CHEBI:57416) is a a D-alpha-amino acid (CHEBI:59871)
• pyruvate (CHEBI:15361) is a a 2-oxocarboxylate (CHEBI:35179)

All other participants of these two reactions are identical, therefore RHEA:22688 is a RHEA:21816.

For reactions that have been classified in this way, the more general and/or specific form(s) of the reaction (aka as parent and child reactions) are shown in the Related reactions section of the website's reaction pages.

Example: RHEA:10144

Note that a reaction may have several parent reactions (see RHEA:10824).

All reaction relationships can be downloaded from our FTP site.

Related documents

• Reaction curation