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 Mn(2+) in preference to Mg(2+). The K(m) value for isopentenyl pyrophosphate is 4x10(-6)m. 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.

Isoprenoid Enzyme Systems of Silkworm. I. Partial Purification of Isopentenyl Pyrophosphate Isomerase, Farnesyl Pyrophosphate Synthetase, and Geranylgeranyl Pyrophosphate Synthetase1

“…These enzymes showed many properties different from those of the corresponding enzymes isolated from mammalian sources. The rather broad pH optimum at the pH range of 7 to 8 of isopentenyl pyrophosphate isomerase from silkworm is different from that of pig liver enzyme, which shows a maximum activity at pH 6.0 to 6.6 (11)(12)(13). The molecular weight of the isopentenyl pyrophosphate isomerase is less than half of that from pig liver (72).…”

Bisphosphonate Inhibitors Reveal a Large Elasticity of Plastidic Isoprenoid Synthesis Pathway in Isoprene-Emitting Hybrid Aspen

“…Yet, why is the possible IDP pool converted to DMADP in dark, but not in light? IDI has a very sharp pH optimum, with changes in pH by one unit reducing the activity of IDI by more than 50% (Holloway and Popják, 1968;Brüggemann and Schnitzler, 2002a). Thus, we suggest that light-dark changes in chloroplastic pH (pH = 8-8.2 in light and pH = approximately 7 in dark) can provide an explanation for changes in IDI activity.…”

“As I remember it” research on biosynthesis of fatty acids, triglycerides, squalene, and cholesterol

“…I had been brooding over those observations for several years and conceived the idea that if prenyl transferase, the enzyme which converts dimethylallyl and isopentenyl pyrophosphate into farnesyl pyrophosphate, were inhibited partially we could divert from the sterol synthetic pathway some intermediates that could be disposed of by an alternative pathway of metabolism. We have made, therefore, an intensive study of the properties of liver prenyl transferase and isopentenyl pyrophosphate isomerase (77,78). In the course of those studies we have found that analogues of geranyl pyrophosphate lacking the a~allylic double bond were powerful inhibitors of prenyl transferase (79), but other analogues containing the ct/3-double bond (such as 6,7-dihydrogeranyl-, cisand trans-3-ethyl-3-methylallyl-, trans-3-propyl-3methylallyl pyrophosphate) were artificial substrates for the enzyme (80)(81)(82).…”