To determine the driving force of protein association, several experiments have been performed separating both domains and changing the linker peptide that keeps them together. In "Plasmodium falciparum", the OPRTase-OMPDCase complex increases the kinetic and thermal stability when compared to monofunctional enzymes. In "H. sapiens", even though separate and fused domains have a similar activity, the former have a higher sensitivity to conditions promoting monomer dissociation. Also, the linker peptide can be removed without inactivating catalysis. In Leishmania donovani, separate OPRTase does not have detectable activity possibly due to lower thermal stability or lack of its linker peptide.