Involved in the biosynthesis of isoprenoids. Catalyzes the 1,3-allylic rearrangement of the homoallylic substrate isopentenyl (IPP) to its allylic isomer, dimethylallyl diphosphate (DMAPP). isopentenyl diphosphate = dimethylallyl diphosphate Competitively inhibited by N,N-dimethyl-2-amino-1-ethyl diphosphate (NIPP) and isopentyl diphosphate. kcat is 17.9 sec(-1) for isomerase activity with IPP (at pH 7.6 and 37 degrees Celsius). Optimum temperature is 60 degrees Celsius. Homooctamer. Dimer of tetramers. Belongs to the IPP isomerase type 2 family.