Isopentenyl-diphosphate:dimethylallyl diphosphate isomerase type 2 (IDI-2) FMN-binding domain. Two types of IDIs have been characterized at present. The long known IDI-1 is only dependent on divalent metals for activity, whereas IDI-2 requires a metal, FMN and NADPH. IDI-2 catalyzes the interconversion of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) in the mevalonate pathway.