Overall, the relative energetics of oxo isomers and isomerization RCs connecting these isomers differ even more significantly between Fe and V hydroxylases than they do for previously studied halogenases. This indicates that vanadyl mimics of native non-heme iron hydroxylases will fail to capture isomerization barriers and energy landscapes accurately. The study of various isomerization RCs sets the stage for targeted approaches to lower active-site isomerization barriers in non-heme iron hydroxylases.