Glyceraldehyde:pyruvate pathway

Maier, W., B. Schneider et al. (1998). Biosynthesis of sesquiterpenoid cyclohexenone derivatives in mycorrhizal barley roots proceeds via the glyceraldehyde 3-phosphate/pyruvate pathway. Tetrahedron Lett. 39(7) 521-524. 

Disch, A., Schwender, J., Muller, C., Lichtenthaler, H.K., and Rohmer, M., Distribution of the mevalonate and glyceraldehyde phosphate/pyruvate pathways for isoprenoid biosynthesis in unicellular algae and the cyanobacterium Synechocystis PCC 6714, Biochem.., 333, 381, 1998. 

Figure 5.4 Outline of the newly discovered glyceraldehyde phosphate/pyruvate pathway for the formation of C5 isoprenoid units. None of the intermediates after 2-C-methyl-D-erythritol 4-phosphate is known. P indicates a phosphate moiety. TPP, thiamine pyrophosphate NADP, nicotinamide adenine dinucleotide phosphate.

In bacteria and plastids of plants, formation of prenyl pyrophosphates, which are the precursors of carotenoids, proceeds via an alternative—the glyceraldehyde-3-phosphate pyruvate pathway. The pathway is apparently the sole source of isoprenoid compounds for the unicellular algae Scenedesmus (Metzler 2003). Initially, pyruvate is decarboxylated by a l-deoxyxylulose-5-phosphate synthase and condensed with D-glyceraldehyde 3-phosphate to form 1-deoxyxylulose 5-phosphate. This product may be the branching point for independent routes to isopentyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). 

At the beginning of the MEP pathway, the glycolytic products, pyruvate and D-glyceraldehyde (GAP), are condensed in a transketolase reaction to deoxy-xylulose phosphate (DXP) by the deoxy-xylulose phosphate synthase (DXS) enzyme. DXP is the precursor for other pathways leading to pyridoxal and thiamine. 

There are two distinct pathways for biosynthesis of the IPP and DMAPP the mevalonate (MVA) pathway and the DXP pathway (Figure 12.3). The MVA pathway functions primarily in eukaryotes, while the DXP pathway is typically present in prokaryotes and the plastids of plants [90,91]. The first reaction in the DXP pathway is the condensation of pyruvate and D-glyceraldehyde-3-phosphate (G3P) to form DXP, which is catalyzed by DXP synthase encoded by the gene dxs [92]. In the second step, DXP is reduced to 2-C-methyl-D-erythritol-4-phosphate (MEP) by DXP reductoisomerase, which is encoded by the gene dxr (ispC) in E. coli. An array of other enzymes encoded by is pi), ispE, ispF, ispG, and ispH act in subsequent sequential reactions, leading to the conversion of MEP to IPP and DMAPP, which are interconverted by the enzyme encoded by idi [93-97],... 

Rohmer, M., Seemann, M., Horbach, S. et al. (1996) Glyceraldehyde 3-phosphate and pyruvate as precursors of isoprenic units in an alternative non-mevalonate pathway for terpenoid biosynthesis. Journal of the American... 

SCHWENDER, J., SEEMANN, M LICHTENTHALER, H.K., ROHMER, M., Biosynthesis of isoprenoids (carotenoids, sterols, prenyl side-chains of chlorophylls and plastoquinone) via a novel pyruvate/glyceraldehyde 3-phosphate non-mevalonate pathway in the green alga Scenedesmus obliquus, Biochem. J., 1996, 316, 73-80. 

Figure 11.2 Pathway for conversion of fructose to acetyl-CoA. The enzyme fructokinase phosphorylates fructose to form fructose 1-phosphate. (The enzyme is present only in the liver.) Fructose 1-phosphate is cleaved by aldolase to form glyceraldehyde and dihydroxyacetone phosphate. Glyceraldehyde is phos-phorylated to form glyceraldehyde 3-phosphate, catalysed by the enzyme triokinase. Dihydroxyacetone phosphate is converted to glyceraldehyde 3-phosphate, catalysed by the isomerase. Glyceraldehyde 3-phosphate is converted to pyruvate by the glycolytic reactions (Chapter 6).

Phospho-2-keto-3-deoxygluconate aldolase, an enzyme in the Entner-Doudoroff pathway, that catalyzes the cleavage 6-phospho-2-keto-3-deoxy-D-gluconate to form pyruvate and D-glyceraldehyde 3-phosphate. 

Terpenes, biogenetically, arise from two simple five-carbon moieties. Isoprenyl-diphosphate (IPP) and dimethylallyldiphosphate (DMAPP) serve as universal precursors for the biosynthesis of terpenes. They are biosynthesised from three acetylcoenzyme A moieties through mevalonic acid (MVA) via the so-called mevalonate pathway. About 10 years ago, the existence of a second pathway leading to IPP and DMAPP was discovered involving l-deoxy-D-xylulose-5-phos-phate (DXP) and 2C-methyl-D-erythritol-4-phosphate (MEP). This so-called non-mevalonate or deoxyxylulose phosphate pathway starts off with the condensation of glyceraldehyde phosphate and pyruvate affording DXP. Through a series of reactions as shown in Fig. 4.1, IPP and DMAPP are formed, respectively [3,7, 42, 43]. 

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