Membrane bound proteins continue to be to date the most elusive molecules in nature, since they are only functional in the lipid bilayer. We have developed a method to study membrane bound proteins at surfaces using nanodiscs films. We have focused our attention to an enzyme complex producing dhurrin, since this is a model of high value pharmaceutical compounds produced by plants. In particular, we study two cytochrome P450 enzymes that catalyse the reaction of tyrosine into a dhurrin precursor. Despite being very similar in amino-acid structure, they differ largely in substrate specificity. We hypothesise that these differences are due to the specific conformation that the proteins undertake at the lipid membrane. Here we apply neutron reflection and use a series of native and mutant enzymes to corroborate our hypothesis.