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 Inhibited by 3,4-epoxy-3-methylbutyl diphosphate (EIPP). kcat is 191 sec(-1) for isomerase activity with IPP. Optimum pH is between 7 and 7.2. Optimum temperature is between 85 and 95 degrees Celsius. Homooctamer. Dimer of tetramers. Belongs to the IPP isomerase type 2 family.