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.[1]References
- The shikimate pathway. III. 3-dehydroquinate synthetase of E. coli. Mechanistic studies by kinetic isotope effect. Le Maréchal, P., Azerad, R. Biochimie (1976) [Pubmed]
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