Isopentenyl pyrophosphate isomerase from liver

Abstract

Isopentenyl pyrophosphate isomerase (EC 5.3.3.2) was purified from extracts of pig liver by ammonium sulphate fractionation and by gel filtration. After about 20-fold purification the preparations were free of phosphatase and prenyltransferase (EC 2.5.1.1), the two enzymes that could have interfered with the assays. The isomerase has a distinct pH optimum at 6·0 and is activated by Mn2+ in preference to Mg2+. The Km value for isopentenyl pyrophosphate is 4×10−6m. The equilibrium of the reaction favours the formation of dimethylallyl pyrophosphate. The reversibility of the isomerase reaction was demonstrated directly by the formation of isopentenyl pyrophosphate from dimethylallyl pyrophosphate. It is suggested that two prenyl isomerases might exist, one involved in the synthesis of trans- and another in the synthesis of cis-polyprenyl substances.