Stereochemistry of the 3-Deoxy-d-arabino-heptulosonate 7-Phosphate Synthetase Reaction and the Chorismate Synthetase Reaction
1972; Elsevier BV; Volume: 247; Issue: 3 Linguagem: Inglês
10.1016/s0021-9258(19)45669-x
ISSN1083-351X
AutoresHeinz G. Floss, D. K. Onderka, M.J. Carroll,
Tópico(s)Enzyme Structure and Function
ResumoAbstract (Z)- and (E)-[3-3H]P-enolpyruvate were prepared from [1-3H]glucose and [1-3H]mannose with the glycolytic enzymes and were converted into shikimates tritiated at C-6 with non-labeled erythrose-4-P and cell-free extract of Escherichia coli mutant 83-24. Degradation to malate and analysis by the fumarase reaction showed that (Z)-[3-3H]P-enolpyruvate had produced [6-3H]shikimate of predominantly 6R configuration and the E isomer had given predominantly (6S)-[6-3H]shikimate. The DAHP synthetase reaction therefore is stereospecific with respect of C-3 of P-enolpyruvate, involving si attack at this center. As a consequence, the transient formation of a methyl group at C-3 of P-enolpyruvate as part of the reaction, as proposed by DeLeo and Sprinson ((1968) Biochem. Biophys. Res. Commun., 32, 873), is unlikely. Further conversion of (6R)- and (6S)-[6-3H]shikimate into chorismate showed that the pro-6R hydrogen is eliminated in this process. Thus, the 1,4-conjugate elimination of phosphoric acid in the chorismate synthetase reaction is anti, rendering a concerted (E2') mechanism unlikely.
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