The function of IDI1 (isopentenyl-diphosphate delta isomerase 1, Ensembl gene identifier ENSG00000067064) is as follows. Catalyzes the 1,3-allylic rearrangement of the homoallylic substrate isopentenyl (IPP) to its highly electrophilic allylic isomer, dimethylallyl diphosphate (DMAPP). .