Human dihydroorotate dehydrogenase (DHODH) is a membrane-bound enzyme of clinical interest and a well-validated drug target for e.g. rheumatoid arthritis and multiple sclerosis. The exact way in which DHODH interacts with membrane-bound ubiquinone (coenzyme Q10) and with inhibitors is not known. Our goal is to use investigate the mechanisms by which DHODH interacts with ubiquinone, with lipids and with inhibitors in planar lipid bilayers mimicking the composition of the inner mitochondrial membrane. We have carried out preliminary neutron reflectivity experiments at the ILL to investigate the structure of supported lipid bilayers made from synthetic lipids and yeast membranes containing ubiquinones Q2 and Q10. The aim of this experiment is to study the interaction of the catalytic domain of DHODH with ubiquinones Q2 and Q10 in model lipid bilayers.