Pyrophosphomevalonate decarboxylase EC

The enzyme catalyzes the simultaneous dehydration and decarboxylation of mevalonate-5-pyrophosphate to isopentenyl pyrophosphate. 

This enzyme has been isolated from a variety of tissues and purified to homogeneity from chicken liver [41,42], The enzyme has a molecular weight of 85 400 and is apparently composed of 2 identical subunits. It is absolutely specific for ATP and will accept either Mg or Mn as the divalent cation. Recently evidence has been presented that an arginyl residue is essential for catalytic activity [43]. Again, no evidence has been presented for any covalently linked enzyme-substrate intermediates. 

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Full details have appeared of the rubber enzyme phosphomevalonate kinase (EC 2.7.4.2) and 5-pyrophosphomevalonate decarboxylase (EC 4.1.1.33). 

Several of the individual enzymes of the early steps of terpene biosynthesis have been isolated. Mevalonic kinase [EC 2.7.1.36, (1) — (2)] has been prepared from several sources, for example Phaseolus vulgaris and pig liver. A feed-back control mechanism was suggested for the animal enzyme. Kekwick determined detailed kinetic data for pyrophosphomevalonate decarboxylase [EC 4.1.1.33,... 

Pyrophosphomevalonate decarboxylase (EC 4.1,1.33 di-phosphomevalonate decarboxylase) 3-Carboxy-cis-cis-muconate cyclo-isomerase (EC 5.5.I.2)... 

The conversion of mevalonate (1) to isopentenyl pyrophosphate (IPP) (4) involves two consecutive phosphorylations at position 5 by successive action of mevalonate kinase (EC 2.7.4.2) and a decarboxylation and dehydration of the tertiary alcohol group by mevalonate 5-pyrophosphate decarboxylase (EC 4.1.1.33) (Fig. 18.4) (Crotean Johnson, 1985 Gershenzon and Croteau, 1990). One mole of ATP is required for each phosphorylation reaction. Mevalonate kinase converts mevalonic acid to (5/ )-phosphomevalonate (5). The second phosphorylation is catalyzed by phospho-mevalonate kinase. The subsequent decarboxylation and dehydration is mediated by the enzyme mevalonate diphosphate decarboxylase (di- or pyrophosphomevalonate decarboxylase EC 4,1.1.3.3) this enzyme requires Mg " or Mn + and ATP for activity (Beale and MacMillan, 1988 Harrison, 1988). All three of these enzymes are found in a number of plants. 

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