Erythrose phosphate

The TK-catalyzed reaction requires the presence of thiamine pyrophosphate and Mg " as cofactors. Although the substrate specificity of the enzyme has not been thoroughly investigated, it has been shown that the enzyme accepts a wide variety of 2-hydroxyaldehydes including D-glyceraldehyde 3-phosphate [591-57-1], D-glyceraldehyde [453-17-8], D-ribose 5-phosphate /47(9(9-2%/7, D-erythrose 4-phosphate and D-erythrose [583-50-6] (139,149—151). 

C-labeled carbon dioxide is administered to a green plant, and shortly thereafter the following compounds are isolated from the plant 3-phosphoglycerate, glucose, erythrose-4-phosphate, sedoheptulose-l,7-bisphosphate, ribose-5-phosphate. In which carbon atoms will radioactivity be found ... 

The transaldolase functions primarily to make a useful glycolytic substrate from the sedoheptulose-7-phosphate produced by the first transketolase reaction. This reaction (Figure 23.35) is quite similar to the aldolase reaction of glycolysis, involving formation of a Schiff base intermediate between the sedohep-tulose-7-phosphate and an active-site lysine residue (Figure 23.36). Elimination of the erythrose-4-phosphate product leaves an enamine of dihydroxyacetone, which remains stable at the active site (without imine hydrolysis) until the other substrate comes into position. Attack of the enamine carbanion at the carbonyl carbon of glyceraldehyde-3-phosphate is followed by hydrolysis of the Schiff base (imine) to yield the product fructose-6-phosphate. 

One of the following molecules (a)-(d) is D-erythrose 4-phosphale, an intermediate in the Calvin photosynthetic cycle by which plants incorporate C02 into carbo- hydrates. If D-erythrose 4-phosphate has R stereochemistry at both chirality centers, which of the structures is it Which of the remaining three structures is the enantiomer of D-erythrose 4-phosphate, and which are diastereomers ... 

One of the steps in the pentose phosphate pathway for glucose catabolism is the reaction of sedoheptulose 7-phosphate with glyceraldehyde 3-pho phate in the presence of a transaldolase to yield erythrose 4-phosphate and fructose 6-phosphate. 

Transaldolase is a dimer with a molecular mass of about 70 000. The fructose 6phosphate molecule produced by this reaction enters the glycolysis, while erythrose 4-phosphate is used as a substrate at the subsequent steps of the cycle. 

Transfer of glycolic aldehyde from xylulose 5-phosphate onto erythrose 4-phosphate or the second transketloase reaction. This reaction is related to the first transketolase reaction and is catalyzed by the same enzyme. The only distinction is that erythrose 4-phosphate acts as an acceptor for glycolic aldehyde ... 

The enzyme also catalyzes the reversible reaction of dihydroxyacetone phosphate with D-erythrose 4-phosphate to produce D-oZ[Pg.218]

D-alJro-Heptulose 7-phosphate + D-glycerose 3-phosphate D-fructose 6-phosphate + D-erythrose 4-phosphate... 

In the experience of the present author, minor deviations from this procedure may result in decreased yields. Oxalacetic acid of high quality is essential, and this should be verified by a melting-point determination prior to use. Decarboxylation of oxalacetate has been reported111 to occur rapidly at pH 7, and it should be kept to a minimum by maintaining the pH as close to 10 as possible when dissolving the oxalacetic acid. A modification of the Comforth reaction is the co-balt(II)-ion-catalyzed condensation of D-erythrose 4-phosphate with oxalacetate to give 3-deoxyheptulosonic acid 7-phosphate112 (as a mixture of the arabino and ribo isomers). Other procedures for the preparation of KDO will be discussed in subsections 3 and 4 of this Section. 

Deoxy-araWno-heptulosonic acid 7-phosphate (10) is a metabolic intermediate before shikimic acid in the biosynthetic pathway to aromatic amino-acids in bacteria and plants. While (10) is formed enzymically from erythrose 4-phosphate (11) and phosphoenol pyruvate, a one-step chemical synthesis from (11) and oxalacetate has now been published.36 The synthesis takes place at room temperature and neutral pH... 

Then, in what is formally a reverse of this reaction, this carbanion equivalent can attack another aldose, such as erythrose 4-phosphate, extending its chain... 

Serine 1 1 glycerate 1 Glyco- lysis 1 1 1 1 Erythrose 4-phosphate... 

T) Ribulose 1,5-bisphosphate (2 Carbon dioxide (3) 3-Phosphoglycerate (4 1,3-Bisphosphoglycerate (5 Clyceraldehyde 3-phosphate Dihydroxyacetone phosphate (7) Fructose 1,6-bisphosphate Fructose 6-phosphate (9) Erythrose 4-phosphate Sedoheptulose 1,7-bisphosphate ( Sedoheptulose 7-phosphate Xylulose 5-phosphate Ribose 5-phosphate Ribulose 5-phosphate ( ) Glucose 6-phosphate... 

Ribose 5-phosphate ) Xylulose 5-phosphate (1 Sedoheptulose 7-phosphate Glyceraldehyde 3-phosphate (1 Erythrose 4-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate Glycerone-3-phosphate... 

D-Erythrose-4-phosphate = D-Arabinose-5-phosphate = N -Acetyl-D-mannosamin-6-phosphate... 

Transaldolase, which catalyzes reactions with d-erythrose 4-phosphate and D-fructose 6-phosphate as substrates. As in the case of fructose-1,6-bisphosphate aldolase, this enzyme uses a e-amino side-chain to form a Schiff base intermediate. In this case, however, the triose phosphate moiety is not released but is transferred to the other aldose (in this case, the aldotetrose). 

This enzyme [EC 5.1.3.1] (also known as phosphoribu-lose epimerase, erythrose-4-phosphate epimerase, and pentose-5-phosphate 3-epimerase) catalyzes the interconversion of D-ribulose 5-phosphate and D-xylulose 5-phosphate. The enzyme can also act on D-erythrose 4-phosphate. 

This enzyme [EC 2.2.1.2], also known as dihydroxy acetone transferase and glycerone transferase, catalyzes the reversible reaction of sedoheptulose 7-phosphate with D-glyceraldehyde 3-phosphate to produce D-erythrose 4-phosphate and o-fructose 6-phosphate. 

RIBULOSE-5-PHOSPHATE 3-EPIMERASE Erythrose-4-phosphate epimerase,... 

The shikimate pathway begins with a coupling of phosphoenolpyruvate (PEP) and D-erythrose 4-phosphate to give the seven-carbon 3-deoxy-D-arabino-heptulo-sonic acid 7-phosphate (DAHP) through an aldol-type condensation. Elimination of phosphoric acid from DAHP, followed by an intramolecular aldol reaction, generates the first carbocyclic intermediate, 3-dehydroquinic acid. Shikimic acid (394) is... 

Alkaloid biosynthesis needs the substrate. Substrates are derivatives of the secondary metabolism building blocks the acetyl coenzyme A (acetyl-CoA), shikimic acid, mevalonic acid and 1-deoxyxylulose 5-phosphate (Figure 21). The synthesis of alkaloids starts from the acetate, shikimate, mevalonate and deoxyxylulose pathways. The acetyl coenzyme A pathway (acetate pathway) is the source of some alkaloids and their precursors (e.g., piperidine alkaloids or anthraniUc acid as aromatized CoA ester (antraniloyl-CoA)). Shikimic acid is a product of the glycolytic and pentose phosphate pathways, a construction facilitated by parts of phosphoenolpyruvate and erythrose 4-phosphate (Figure 21). The shikimic acid pathway is the source of such alkaloids as quinazoline, quinoline and acridine. 

Structure with erythrose 4-phosphate bound a) U. Nilsson, L. Meshalkina, Y. Lindqvist, G. Schneider, /. Biol. Chem. 1997, 272,1864-1869 b) C. Wikner, U. Nilsson, L. Meshalkina, C. Udekwu, Y. Lindqvist, G. Schneider, Biochemistry 1997, 36, 15 643-15 649. c) model of donor bound G. Schneider, Y. Lindqvist, Biochim. Biophys. Acta 1998, 1385, 387-398. 

All carbons are derived from either erythrose 4-phosphate (light purple) or phosphoenolpyruvate (pink). Note that the NAD+ required as a cofactor in step (3) is released unchanged it may be transiently reduced to NADH during the reaction, with formation of an oxidized reaction intermediate. Step (6) is competitively inhibited by glyphosate (COO—CH2—NH—CH2—PO ), the active ingredient in the widely used herbicide Roundup. The herbicide is relatively nontoxic to mammals, which lack this biosynthetic pathway. The chemical names quinate, shikimate, and chorismate are derived from the names of plants in which these intermediates have been found to accumulate. 

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