Isopentenyl diphosphate (IPP) isomerase, a member of the Nudix hydrolase superfamily, is a key enzyme in the isoprenoid biosynthetic pathway. Isoprenoids comprise a large family of natural products including sterols, carotenoids, dolichols and prenylated proteins. These compounds are synthesized from two precursors: isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). IPP isomerase catalyzes the interconversion of IPP and DMAPP by a stereoselective antarafacial transposition of hydrogen. The enzyme requires one Mn2+ or Mg2+ ion in its active site to fold into an active conformation and also contains the Nudix motif, a highly conserved 23-residue block (GX5EX7REUXEEXGU, where U = I, L or V), that functions as a metal binding and catalytic site. The metal binding site is present within the active site and plays structural and catalytical roles. IPP isomerase is well represented in several bacteria, archaebacteria and eukaryotes, including fungi, mammals and plants. Despite sequence variations (mainly at the N-terminus), the core structure is highly conserved.