The shikimate pathway. III. 3-dehydroquinate synthetase of E. coli. Mechanistic studies by kinetic isotope effect.
The conversion of 3-deoxy D-arabino heptulosonate 7-phosphate to 3-dehydroquinate by the 3-dehydroquinate synthetase from E. coli is characterized by a low but significant kinetic isotope effect for tritium carried in position-5 of DAHP, while no isotope effect was detectable for tritium in position-4. This effect was observed at different pH nad is interpreted as a result of theintermediary of a 5-ketonic form of the substrate, formed in a preliminary non limiting step during the enzymic cyclization reaction. A tentative scheme for the 3-DHQ synthetase reaction is proposed involving five steps: oxidation by NAD+ in position-5, phsophate elimination after enolization, reduction with precedently formed NADH and cyclization by attack of the 2-carbonyl by the C-7 methylene group.
D055598:Chemical Phenomena; D002621:Chemistry; D004926:Escherichia coli / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008025:Ligases / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D010710:Phosphates / Q000378:metabolism; D019761:Phosphorus-Oxygen Lyases; D011801:Quinic Acid / Q000031:analogs & derivatives / Q000096:biosynthesis; D012765:Shikimic Acid / Q000096:biosynthesis; D013403:Sugar Phosphates / Q000378:metabolism; D014316:Tritium
D010710:Phosphates; D013403:Sugar Phosphates; D011801:Quinic Acid; D009243:NAD; D014316:Tritium; D012765:Shikimic Acid; C020001:3-dehydroquinate synthetase; D019761:Phosphorus-Oxygen Lyases; D008025:Ligases