Vectorial representation of chemical compounds and enzymatic activities. (A) Example of an oxidation reaction (R-OH → R = O) included in KEGG. The components of the enzyme vector (which is the difference between the vectors of the product and substrate) to some extent reflect the nature of the transformation: loss of 2 HCC, 1 OCH and 1 HOC triplets. On the left, a 3D projection of the 60-dimensional space defined by the compound and enzyme vectors is depicted, with some compounds, reactions and pathways shown. (B) Representation of the vectors within the KEGG dataset. Both reactions and compounds are defined by 60-D vectors where each component represents an atom triplet.