Isopentenyl pyrophosphate isomerase from pig liver |
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Authors: | Derek V. Banthorpe Shawn Doonan Jan A. Gutowski |
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Affiliation: | Christopher Ingold Laboratories, Department of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, United Kingdom |
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Abstract: | Isopentenyl pyrophosphate isomerase (EC 5.3.3.2) from pig liver has been purified 197-fold. The preparation was estimated to contain less than 10% of contaminating protein. The molecular weight determined by gel filtration was 82,500 ± 3,000 and the isoelectric point from isoelectric focusing was in the range 6.0–6.2. N-terminal analysis showed the presence of both leucine and proline. The pH optimum of the enzyme preparation was 6.3. After dialysis against EDTA, activity was restored by either Mn2+ or Mg2+, the former being more effective. At the optimum pH and concentration of Mn2+, Km and V were 2.7 μm and 6.7 μmol min?1 mg?1, respectively. The enzyme was partially inhibited by a variety of terpene mono- and pyrophosphate esters, by inorganic phosphate ions, and by acetate ions; essentially complete inhibition by sulfhydryl-blocking reagents was observed. ATP partially inhibited, the degree of inhibition showing a sigmoid dependence on ATP concentration. Monothiols and dithiothreitol activated the enzyme, as did mevalonic acid. |
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