Erythrulose-1-phosphate

Other challenges arise when using metabolites from different branches of metabolism. For example, the production of shikimates requires phospho-enolpyruvate, an intermediate of glycolysis, and erythrulose 4-phosphate, an intermediate. It is uncertain whether the fluxes of these would be properly balanced if the attempt were made to overexpress the shikimate pathway. In glucose medium, the production of DAHP was significantly improved by the expression of Pps as it increases the availability of PEP [30, 31,184]. 

The p3nranose or furanose structure of the esters appears to influence the rate of hydrolysis. Thus glucose 6-phosphate which can form a pyranose ring is more stable than fructose 6-phosphate which can only form a furanose ring. The acid lability of some compounds such as glycolaldehyde phosphate , erythrose 4-phosphate and erythrulose phosphate may be partly due to the fact that they cannot form ring structures. Furthermore ribose 5-phosphate is more stable than ribulose 5-phosphate and in this case the difference is presumably due to the fact that the former can form a furanose ring while the latter can only exist in the linear form. 

Erythrulose phosphate. An ester of erythrulose, presumably the i-phos-phate, has been obtained by enz5miic condensation of triose phosphate and formaldehyde. ... 

TK activity was determined by a spectrophotometric assay at 340 nm. In 0.5 mL of tris buffer (50 mM) pH 7.6, were added 50 pL of L-erythrulose from a 1 m stock solution in water (0.05 mmol), 25 pL of o-ribose-5-phosphate from a 160 him stock solution in water (4.0 pmol), 5 pC of ThDP from a 21 mM stock solution in water (0.1 pmol), 10 pL of MgCl2 from a 50 mM stock solution in water (0.5 /rmol), 10 pL of NADH from a 14 him solution in water (0.14 /imol), alcohol dehydrogenase (12 units). 

Lower monosaccharides, i.e., aldo- and keto-bioses, -trioses, and -tetroses, do not exist naturally in a free state. Glyceroaldehyde and hydroxyacetone in phospho-rylated forms are the products of alcoholic fermentation and glycolytic sequence. Erythrose and erythrulose also appear in phosphorylated forms in the pentose cycle of glucose, while ketopentose-ribulose can be found as its phosphate ester (Table 5.1). 

Tetrose a monosaccharide containing four carbon atoms, e.g. threose, erythrulose. T. occur as intermediates in carbohydrate metabolism, usually as their phosphates. 

The specificity of purified transketolase is rather broad, and several compounds have been shown (93) to act as donors of active glycolaldehyde. Included in these compounds are D-ribulose 5-phosphate, D-sedoheptulose 7-phosphate, D-fructose 6-phosphate, L-erythrulose, and hydroxypyruvic acid. A number of aldehydes have been shown to act as active glycolalde-... 

For synthetic purposes hydroxypyruvate 119 can effectively replace the natural donor components [258]. Its covalent activation occurs at a reduced rate of about 4% relative to xylulose 5-phosphate (121) but is accompanied by spontaneous decarboxylation [262]. Thus, loss of carbon dioxide renders synthetic reactions irreversible whereas alternative donors, for example l-erythrulose, require coupling to cofactor recycling to shift the overall equilibrium [263]. The thermodynamic driving force from decarboxylation of 119 is particularly useful with equilibrating multi-enzyme systems such as that used in the gram-scale synthesis of two equivalents of 121 from 42 (Figure 5.54) [264]. 

Tetroses. Both threose and erythrose have already been mentioned (formulas in Section 1). The ketose erythrulose should be mentioned because it appears as an intermediate in several biochemical transformations (among others in photosynthesis) in the form of its phosphate. 

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