and proteins) stem from BRENDA entries classified as "natural substrate/product pair". Fig. depicts the number of mapped reactions per EC class, split into overall (outer circle), balanced (second circle) and mapped (inner circle) reactions, after all pre-and post-processing steps. We find that no EC class exhibits a disproportionally large number of imbalanced reactions or failed mappings, and that En-zymeMap is mainly comprised of reactions in the EC classes 1 (oxidoreductases), 2 (transferases) and 3 (hydrolases) to nearly equal amounts, whereas the EC classes 4 (lyases), 5 (isomerases) and 6 (ligases) only make up about 10% of all reactions in total. Translocases (EC 7) were not considered for mapping, since they catalyze the movement of ions or molecules across membranes, so that the reactant and product molecules are usually the same.