title: The enzymes forming isopentenyl pyrophosphate from 5-phosphomevalonate (mevalonate 5-phosphate) in the latex of Hevea brasiliensis.
abstract: 1. Phosphomevalonate kinase and 5-pyrophosphomevalonate decarboxylase have been purified from the freeze-dried latex serum of the commercial rubber tree Hevea brasiliensis. 2. The phosphomevalonate kinase was acid- and heat-labile and required the presence of a thiol to maintain activity. 3. The 5-pyrophosphomevalonate decarboxylase was relatively acid-stable and more heat-stable than the phosphokinase. 4. Maximum activity of the phosphokinase was achieved at pH 7.2 with 0.2mm-5-phosphomevalonate (K(m) 0.042mm), 2.0mm-ATP (K(m) 0.19mm) and 8mm-Mg(2+) at 40 degrees C. The apparent activation energy was 14.8kcal/mol. 5. Maximum activity of 5-pyrophosphomevalonate decarboxylase was achieved at pH5.5-6.5 with 0.1mm-5-pyrophosphomevalonate (K(m) 0.004mm), 1.5mm-ATP (K(m) 0.12mm) and 2mm-Mg(2+). The apparent activation energy was 13.7kcal/mol. The enzyme was somewhat sensitive to inhibition by its products, isopentenyl pyrophosphate and ADP.
mesh_terms: D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate / Q000378:metabolism; D000475:Alkenes / Q000096:biosynthesis*; D002262:Carboxy-Lyases / Q000302:isolation & purification / Q000378:metabolism; D002845:Chromatography; D002850:Chromatography, Gel; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008798:Mevalonic Acid / Q000378:metabolism*; D010756:Phosphoric Acids / Q000096:biosynthesis* / Q000378:metabolism; D010770:Phosphotransferases / Q000302:isolation & purification / Q000378:metabolism*; D010944:Plants / Q000201:enzymology; D012408:Rubber; D013455:Sulfur
chemical_list: D000475:Alkenes; D010756:Phosphoric Acids; D000244:Adenosine Diphosphate; D013455:Sulfur; D000255:Adenosine Triphosphate; D012408:Rubber; D010770:Phosphotransferases; D002262:Carboxy-Lyases; D008798:Mevalonic Acid