Abstract
Abstract (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.
Highlights
[l-3H]glucose and [l-sH]mannose with the glycolytic enzymes and were converted into shikimates tritiated at C-6 with nonlabeled erythrose-4-P and cell-free extract of Escherichia coli mutant 83-24
In this paper we report on the steric course of two reactions of the shikimic acid pathway, the formation of 3
[%]shikimic acid has usually been prepared by photosynthesis using leaves of Ginkgo biloba and WO2 (e.g. Reference 39) or, in one case, by a five-step chemical synthesis starting from methyl [2,3-Wlacrylate (40)
Summary
M- and (E)-[3-3H]P-enolpyruvate were prepared from [l-3H]glucose and [l-sH]mannose with the glycolytic enzymes and were converted into shikimates tritiated at C-6 with nonlabeled erythrose-4-P and cell-free extract of Escherichia coli mutant 83-24. The 1,4-conjugate elimination of phosphoric acid in the chorismate synthetase reaction is anti, rendering a concerted (E2’) mechanism unlikely. The &ikimic acid pathway is the main biosynthetic route leading to the formation of aromatic compounds in higher plants and microorganisms. It is involvedint,he biosynthesisof such essential compomitls as the aromatic amino acids phenylalanine, tyrosine, and trvpiophan, a number of quinones, e.g. ubiquinone, plastoquinonc, vitamin K, and the tocopherols, and the vitamin folic acid as well as in the formation of a vast number of so-called secondary metabolites, like many alkaloids, plant phenols, and a number of antibiotics. In this paper we report on the steric course of two reactions of the shikimic acid pathway, the formation of 3-. Preliminary accounts of this work have been published (8, 9)
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