We are presenting a reaction driven by a biocatalyst to show how reaction SPL can handle catalysts and biomolecules, something that is clearly beyond the capability of molfiles and RXN. We are using one of the best studied enzymatic reactions, the lactate dehydrogenase (LDH) for which there are crystallographic structure models published by Cook and Senkovich under the PDB accession numbers 4ND4 and 4ND3. The Reaction SPL file is "reaction-LDH-multistep.xml" in the supplementary material ZIP file. The LDH reaction is reversible, pyruvate + NADH ↔ L-lactate + NAD + with the lactate dehydrogenase as the catalyst. and in the direction of L-lactate as a product shows how stereo-selective enzymatic reactions happen by observing the details of the intermediate structures from the PDB files 4ND4 for the LDH-pyruvate-NADH complex and 4ND3 for the LDH-L-lactate-NAD + complex. The molfiles of the NAD ligand complexes were extracted with JSmol from the original PDB entries, to reproduce the figure from ref. . The NAD in the molfile of 4ND3 (pyruvate) was changed to NADH by manually editing 3 bond valences and having JSmol calculate hydrogens at the apex of NADH (atom position 2 in Figure ). Then for each molfile the InChI identifier was generated and atoms in the molfile rearranged to follow the canonical InChI atom numbers.