Human Isopentenyl Diphosphate:Dimethylallyl Diphosphate Isomerase: Overproduction, Purification, and Characterization

Isopentenyl diphosphate (IPP):dimethylallyl diphosphate isomerase catalyzes an essential activation step in the isoprenoid biosynthetic pathway. A human cDNA sequence [J. Xuan, J. Kowalski, A. F. Chambers, and D. T. Denhardt (1994)Genomics20, 129–131] containing a 684-base-pair open reading frame was recently reported that encoded a protein with a significant degree of similarity to two fungal IPP isomerases [F. M. Hahn and C. D. Poulter (1995)J. Biol. Chem.270, 11298–11303]. The human cDNA sequence was cloned into expression plasmid pFMH12. The encoded protein was overproduced inEscherichia coliand purified to >90% homogeneity in two steps by ion-exchange and hydrophobic interaction chromatography. The recombinant protein catalyzed the isomerization of IPP to dimethylallyl diphosphate and was maximally active at pH 7.0 in the presence of Mg2+. The Michaelis constant for IPP was 33 μM, similar to the value of 43 μMreported for yeast IPP isomerase;Vmax= 4.1 μmol min−1mg−1for recombinant human IPP isomerase, approximately fivefold less than reported for the yeast enzyme [I. P. Street and C. D. Poulter (1990)Biochemistry29, 7531–7538].