Pentulose-5-phosphate

In contrast, another group35 found that extracts of E. coli contained a mixture of pentulose phosphates at a concentration near 0.3 nmol per mg of the dry weight of cells. The sugars were estimated by gas chromatography-mass spectrometry after treatment of the extract with phosphatase followed by silylation, or borohydride reduction and acetylation. Furthermore, a partially purified preparation from these extracts catalyzed the synthesis of 1-deoxypentulose... 

Because sugars are involved in most of the mechanisms established for the synthesis of these heterocycles, the development of carbohydrate chemistry has been most helpful in these researches—especially for the preparation of specifically labeled molecules. Conversely, the contribution of these efforts to carbohydrate chemistry and biochemistry has shown the involvement in biosynthesis of 1 -deoxy-D-f/rreo-pentulose—scarcely before recognized and considered a rare sugar—and of fully functionalized pentuloses of still unknown configuration (or their phosphates). Finally, evidence has been found in prokaryotes for a most extraordinary transformation of 5-amino-l-(P-D-ribofuranosyl)imidazole 5 -phos-phate into a pyrimidine. Surely, this transformation should be explained in terms... 

Paper ionophoresis, sugars, Maurice Stacey s work, 17 Pectic acid, 350, 352,414 Pectin, 348, 350-353 Pectinic acid, 353 Pentulose, synthesis, 281 D-cryt/iro-Pentulose 5-phosphate, 289 Peptidoglycans, 167-168 Per-O-acetylated di-D-fructose dianhydride derivatives... 

D-Xylulose 5-phosphate (ii-threo-2-pentulose 5-phosphate, XP) stands as an important metabolite of the pentose phosphate pathway, which plays a key fimction in the cell and provides intermediates for biosynthetic pathways. The starting compound of the pathway is glucose 6-phosphate, but XP can also be formed by direct phosphorylation of D-xylulose with li-xylulokinase. Tritsch et al. [114] developed a radiometric test system for the measurement of D-xylulose kinase (XK) activity in crude cell extracts. Aliquots were spotted onto silica plates and developed in n-propyl alcohol-ethyl acetate-water (6 1 3 (v/v) to separate o-xylose/o-xylulose from XP. Silica was scraped off and determined by liquid scintillation. The conversion rate of [ " C]o-xylose into [ " C]o-xylulose 5-phosphate was calculated. Some of the works devoted to the separation of components necessary while analyzing enzyme activity are presented in Table 9.8. 

D-xylose =i D-Z/ireo-pentulose —> D-ZAreo-pentulose 5-phosphate... 

Subsequent studies196 on crystalline transketolase have revealed the presence of a contaminating enzyme termed pentulose 5-phosphate waldenase (or epimerase) the presence of which had led to the erroneous conclusion that d-erythro-pentulose 5-phosphate was the substrate for transketolase. d-erythro-Pentulose 5-phosphate is virtually unattacked by transketolase prepared from spinach or liver. In subsequent discussions of experiments involving the use of transketolase, in this article, the enzymic reactions must be viewed as the result of action of transketolase and pentulose 5-phosphate waldenase (epimerase). 

D-erythro-Pentulose 5-phosphate (XLIV) has been formed by the action of transketolase on hydroxypyruvate (XLII) and D-glycerose 3-phosphate, the hydroxypyruvate being decarboxylated196 to active glycolaldehyde which then reacts with the triose phosphate by an acyloin reaction.28 The active glycolaldehyde is also formed from L-glycero-tetrulose, d-altro-heptulose 7-phosphate, D-fructose 6-phosphate, and D-i/ireo-pentulose 5-phosphate and it reacts with various aldehydes (acceptors) to give ketoses.198, 200 Thus, substitution of L-gfh/cero-tetrulose for hydroxypyruvate in the above experiment also resulted in formation of D-en/i/iro-pentulose... 

D-lAreo-Pentulose 5-phosphate + D-erythrose 4-phosphate tran>lcetolaM, D-fructose 6-phosphate + D-glycerose 3-phosphate 2 Triose phosphate —> hexose phosphate + inorganic phosphate... 

The tetrose phosphate (LVI) acts as an acceptor for active glycolaldehyde derived from n-i/ireo-pentulose 5-phosphate (LII), and thus, in the presence of transketolase, yields D-fructose 6-phosphate (LV) and D-glyc-erose 3-phosphate. The reverse of this reaction has been observed.200 The... 

With zymohexase, fructose 1,6-diphosphate, and acetaldehyde, a 5-de-oxypentulose 1-phosphate resulted,66 and, with a pea-aldolase preparation, the product was identified as 5-deoxy-D-ilireo-pentulose (LXI). Using... 

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