We then compared the obtained reactions to KEGG and Meta-Cyc after removing atom mappings, and found that of the nearly 48k unique reactions in EnzymeMap, only 0.5k are also found in MetaCyc (0.6k after passing MetaCyc through the EnzymeMap workflow, i.e. also adding reverse reactions), and 1.8k are also found in KEGG (5k after passing KEGG through the EnzymeMap workflow), where we compared the unmapped reaction SMILES strings. EnzymeMap thus provides access to several tens of thousands of reactions not covered by other databases. The workflow furthermore is not limited to BRENDA. With minimal changes to the setup of the initial raw reactions, we were easily able to map reactions from KEGG and MetaCyc, leading to 8.0k and 4.6k mapped reactions, respectively. We distribute those alongside En-zymeMap, since a combination of all sources might be beneficial for future data-driven prediction of enzymatic reactions. For MetaCyc, we were furthermore able to compare the atom mappings distributed with MetaCyc with atom mappings from the EnzymeMap workflow. For reactions that led to a valid mapped reaction with our workflow, we found same mappings for 70% of the reactions (accounting for equivalent mappings due to symmetry). For the reactions with different atom mappings, our mappings had an equal or less number of bond edits than the MetaCyc mappings in 92% of cases. Manual examination of random cases where EnzymeMap lead to better mapping results than the native MetaCyc mappings revealed a few hundred of errors in MetaCyc, with an example shown in Fig. , where five atoms are wrongly mapped. We also found cases where atoms corresponding to different elements (for example phosphorus and carbon) were assigned the same map number. This highlights the need for better atom mapping routines for enzymatic reactions, or at least better post-processing steps to flag erroneous reactions, even for highly curated databases like MetaCyc. However, the EnzymeMap workflow is not without flaws itself, due to missing rules in the employed Broadbelt rule set, leading to possibly wrong mappings or no mappings at all. For the latter case, we compared the number of MetaCyc reactions that could not be mapped via the En-zymeMap workflow per 1-digit EC class, and found that all EC classes are about equally affected by failed mappping attempts. Manual inspection revealed many reactions in MetaCyc, for which no rule exists currently, including multi-step reactions involving different reaction steps (e.g. a reaction followed by decarboxylation), reactions involving changes in rings, some transfer reactions, ring-forming reactions, and hydrolysis of peptide bonds, amongst others. We attempt to address missing rules in a future publication, and thus future versions of EnzymeMap. Since a new rule set only requires to update one file and re-run the workflow, the incorporation of new rules is a trivial exercise. For the remainder of this study (and the current version of EnzymeMap), we stick with the Broadbelt rule set, since the creation and validation of a new rule set is well beyond the scope of the current