KEGG Chemical Function (KCF) format. (a) KEGG Chemical Function (KCF) format of NADPH. KCF format has three sections; ENTRY, ATOM and BOND. ENTRY section describes the KEGG ID and the type of the entry. ATOM section describes the numbering of the atoms, KEGG Atom Types for the labels on the atoms, atomic species (C for carbon, N for nitrogen, etc), and 2D coordinates of the atoms. BOND section describes the numbering of the bonds, the numbering of the two atoms in the bond, and the bond order, and steric configuration of the bond. (b) KCF representation of NADPH. Molecules are represented as graph structures, where nodes represent atoms labeled with KEGG Atom Types.