PEP -dependent

FIGURE 10.26 Glucose transport in E. coli is mediated by the PEP-dependent phosphotransferase system. Enzyme I is phosphorylated in the first step by PEP. Successive phosphoryl transfers to HPr and Enzyme III in Steps 2 and 3 are followed by transport and phosphorylation of glucose. Enzyme II is the sugar transport channel. 

The bacterial phosphoenolpyruvate (PEP)-dependent carbohydrate phosphotransferase systems (PTS) are characterised by their unique mechanism of group translocation. The transported solute is chemically modified (i.e. phos-phorylated) during the process (for comprehensive reviews see [151,152] and... 

Pyruvate-dependent aldolases catalyze the breaking of a carbon-carbon bond in nature. This reaction can, however, be reversed if an excess of pyruvate is used, establishing one new stereocenter in the course of it. The natural function of phosphoenolpyruvate (PEP)-dependent aldolases on the other hand is to catalyze the synthesis of a-keto acids. Since PEP is a very reactive, unstable and difficult to prepare substrate, they are not commonly used in synthesis. 

The first group is the dihydroxyacetone phosphate (DHAP)-dependent aldolases, which use DHAP as the donor to produce 2-keto-l, 3, 4-trihydroxy motifs. The second group, the pyruvate- or phosphoenol pyruvate (PEP)-dependent aldolases, uses pyruvate to form 4-hydroxy-2-ketoacids. The third... 

Scheme 5.28. Phospoenolpyruvate (PEP) dependent aldolases and the reactions they catalyze.

Non-sulfur, purple, photosynthetic bacteria, Rho do spirillum rub-rum and Rhodopseudomonas spheroides172 also possess a PEP-de-pendent D-fructose phosphotransferase. Two protein fractions are required for D-fructose phosphorylation. In contrast to PEP-depend-ent, phosphotransferase systems isolated from other bacteria, the aforementioned two organisms have one active protein fraction tightly associated with the membrane fraction, while another in the crude extract is solubilized by extraction with water, and has a molecular weight of about 200,000. There is no evidence for the presence of a phosphate-carrier protein of low molecular weight like HPr.171,173 The... 

PEP-dependent phosphotransferase enzyme II PEP-sugar phosphotransferase enzyme II PTS permease... 

Figure 11.1 Proposed pathway for hex-ose metabolism of homofermentative LAB (1) and (2) phosphoenolpyruvate (PEP)-dependent sugar phosphotransferase system (PTS) (3) mannitol-specific PTS (4) phospho-glucose isomerase (5) mannitol-1-phosphate dehydrogenase (6) mannitol-1-phosphatase (7) 6-phosphofructokinase (8) fructose-diphosphatase (9) fructose-1,6-diphosphate aldolase (10) triosephosphate isomerase (11) glyceraldehyde-3-phosphate dehydrogenase...

Mannitol-specific enzyme II of the E. coli PEP-dependent phosphotransferase system... 

EC 5.1.3.8). While cascade coupling of the epimerization to a NeuA-catalyzed carboligation suffers from the combination of two unfavorable equilibria [24], the alternative coupling to PEP-dependent NeuS is more productive, as demonstrated by a whole-cell approach to the production of 1 [25]. Also, KDN 3 has been produced on a 100 g scale from D-mannose (8) and 5 using a pilot-scale enzyme membrane reactor with an overall crystallized yield of 75% (Scheme 17.5) [26]. 

Higher organisms and some bacteria utilize PEP-dependent N-acetylneuraminic acid synthase (NeuS EC 2.5.1.56) for the generation of sialic acids and related compounds (Scheme 17.3) [17, 21]. In mammaHan cells, NeuSAc is synthesized from the phosphorylated ManNAc-6-phosphate precursor by the PEP-dependent N-acetylneuraminic acid 9-phosphate synthase (Neu9PS EC 2.5.1.57). By simultaneous release of inorganic phosphate from the enol ester upon C-C bond formation, the additions are essentially irreversible. 

The biosynthetic pathway that produces bacterial cellulose from glucose and fructose is shown in Fig. 14.2. Glucose is phosphorylated by glucose hexokinase and not by the phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS). The resulting glucose-6-phosphate (G6P) is metabolized through the pentose pathway, because the activity of fructose-6-phosphate (F6P) kinase, which phos-phorylates F6P to fructose-1,6-diphosphate (FDP), is absent in acetic acid bacteria. 

Threonine aldolases (ThrA EC4.1.2.5) and serine hydroxymethyltransferases (SHMT EC 2.1.2.1) are pyridoxal-5 -phosphate (PEP) dependent aldolases that catalyze the aldol addition of glydne to aldehydes [155-158], Since two new stereogenic centers are formed, four possible stereoisomers can be formally obtained. However, contrary to the case of DHAP-dependent aldolases, the four set of stereocomplementary enzymes have not been found in nature yet (Scheme 10.7) [157,159,160]. 

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