Schema of the ORENZA relational database. The primary key of each table is in bold underlined type. Dashed arrows indicate references to foreign keys. Plain arrows represent the origin of the data stored in each table. Moreover, for the table Enzyme_activities the origin of the data is indicated by the same color code used to identify each of the following major primary databases used in our analysis: UniProt (purple), BRENDA (blue), ENZYME (green), PDB (orange) and NC-IUBMB (beige).