It catalyzes the reaction from dihydroxyacetone phosphate (DHAP) to glyceraldehyde 3-phosphate (GAP) and is known for its distinctive α/β barrel structure called TIM barrel (see Fig. ). The starting monomer structure is based on the protein crystal structure 7TIM from the PDB with a co-crystallized phopsphoglycolohydroxamic acid (PGH), which is a well-known TIM inhibitor. To get reactant and product staring structures PGH was replaced with DHAP and GAP, respectively, and the structures were processed as described in Section 6. For cryst saaPCVA, the initial structure with PGH was used. The minimal QM region contains only the corresponding ligand, either PGH, DHAP or GAP.