Xylose-5-phosphate

Xylose-1-phosphate, X-84 Xylose-3-phosphate, X-85 Xylose-5-phosphate, X-86 Xylosone, P-45 Xylostacin, X-87 Xylosyl phosphate, X-84 Xylosylamine, X-88 4-(Xylosylamino)benzoic acid, B-6 a-D-Xylosylisoprimeverose, X-59 4-p-Xylosylxylobiose, X-90 Xylotetraose, X-89 Xylothiapyranose, T-99 Xylotriose, X-90 Xylulose, P-48 Xyluronic acid, X-91... 

Migration of the phosphate group can occur on heating with acid through the intramolecular formation of an intermediate cyclic phosphate. All attempts to s)mthesise xylose 3-phosphate from xylose derivatives in which C-5 was substituted led to the preparation of the 5-phosphate. Removal of the C-5 blocking group was followed by the formation of the 3.5-cyclic phosphate (CLXXXVI) and this was cleaved preferentially at the 3 position with the formation of the 5-phosphate (CLXXXVII). Recent studies have revealed References p. 63... 

Migration of the phosphate group may take place after phosphorylation, as in the preparation of D-xylose 3-phosphate . The starting material was 1,2-isopropylidene xylose which on phosphorylation with diphenyl phos-phorochloridate gave the 5-phenyl phosphate. Treatment of the latter with boiUng alkali led to the formation of a 3,5-cyclic phosphate with elimination of one phenyl group. Hydrolysis of the latter gave a mixture of the 3- and 5-D-xylose phosphates. 

When the OH group next to the phosphate is free, a five-membered ring is formed. Thus xylose 3-phosphate gives the 3 4- or 2 3-cyclic phosphate. But if the OH next to the phosphate forms part of a furanose or p nanose References p. 140... 

D-Xylose 3-phosphate is formed from the 5-phenyl phosphate of 1,2-iso-propyhdene xylofuranose which by alkaline treatment gives a3,5-cyclic phosphate. Hydrolysis of the latter yields a mixture of the 3- and 5-phosphates. ... 

In the next reaction, an enzyme called transketolase splits the xylose phosphate to 2-glyceraldehyde phos-... 

Generally speaking, the phosphorylated deoxysugars undergo the usual reactions of carbohydrates without complication. For instance, both 2-deoxy D-ribose 5-phosphate (52, 59) and 2-deoxy D-xylose 5-phosphate (2) can be reduced to the corresponding 2-deoxy d-erythro- (48) and 2-deoxy D-threo-pentitol 5-phosphates (49). 2-deoxy ribose 5-phosphate has also been oxidized (52) to the corresponding phosphorylated acid (50). 

The discrepancy between the behavior of arabinose- and xylose-3, 5-(hydrogen phosphates) probably reflects the difference which exists in the steric arrangement of these two cyclic phosphodiesters. In the xylo-furanose derivative (89), the hydroxyl group on C-3 and the primary hydroxyl group are cis the cyclic phosphate is easily formed and perfectly strainless. In arabinofuranose these same groups are in position trans and, although an apparently strainless molecule can be constructed from models, it is probable that in this case the main ring of the compound will be that formed by the phosphodiester, with a concomitant tendency for the compound to assume the aldehydo form. Objection to... 

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. 

Harrison, Tarr and Hibbert96 investigated the production of levan from sucrose by the action of Bacillus subtilis Cohn and B. mesentericus Trevisan. Nutrient solutions containing 10% carbohydrate, 0.1% peptone, 0.2% disodium hydrogen phosphate and 0.5% potassium chloride were incubated at 37° for six days. Levan formation occurred only with sucrose and raffinose, and not with melezitose, lactose, maltose, D-xylose, D-glucose or D-fructose. It was therefore suggested that only those carbohydrates with a terminal D-fructofuranose residue were satisfactory substrates for levan formation. 

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

Acetaldehyde combines with 2,3-O-isopropylidene-D-glycerose, in the presence of potassium carbonate, to give 2-deoxy-4,5-O-isopropylidene-D-ribose and -D-xylose,46 suggesting a possible biosynthetic route (see Reference 46). The suggestion that 2-deoxy-D- ribose (2-deoxy-D-erythro-pentose) arises by combination of acetaldehyde with D-glycerose 3-phosphate to give 2-deoxy-D-ribose 5-phosphate (LX) was verified by using enzyme... 

The D-xyloketose was prepared by autoclaving at 120° a 10% solution of D-xylose for 45 minutes in the presence of 0.2 M phosphate buffer, pH 6.8. Most of the unreacted D-xylose was separated by crystallization, leaving a sirup consisting chiefly of D-xyloketose. 

Both D-[l- C]xylose and D-[5- C]arabinose were exposed to a concentrated phosphate buffer solution (pH 6.7). 1-Hydroxy-2-propanone (ace-tol) was distilled from the heated solution. Radioassay indicated that similar labeling [3- C] occurred in the acetol from both pentoses, with loss of the configurational difference thus, a 3-ketopentose or its enediol was suggested as an intermediate. Further work with 3-0- and 6-0-methyl-D-glucose and with 1-0-methyl-D-fructose indicated that /3-elimination from a 3-ketose or, in the case of a hexose, from a 3-ketose or a 4-ketose, or both, tautomerization of the resulting a-diketone to a /3-diketone, and hydrolytic cleavage are essential steps in the formation of acetol. 

Figure 3(A). Comparison of temperature optima for activities of glucose isomerase, amylase, and >galactosidase. Enzymes were assayed with cell extract from xylose-grown cells. A 100% activity value corresponds to 0.60, 0.58, and 0.46 U/mg for glucose isomerase, amylase, and -galactosidase, respectively. Cell extracts in 50 mM sodium phosphate buffer (pH 7.0), 100 mM sodium acetate buffer (pH 5.5), and 100 mM sodium phosphate buffer (pH 6.0) for glucose isomerase, amylase, and -galactosidase, respectively, were preincubatcd at the indicated temperatures, prior to the assay for residual enzyme activities. Reprinted with permission from ref. 20. Copyright 1990 American Society for Microbiology.

XYLOGLUCAN SYNTHASE d-XYLONATE DEHYDRATASE XYLOSE ISOMERASE D-Xylose 5-phosphate,... 

These enzymes vary widely in secondary and tertiary structure.1273 Mannose-6-phosphate isomerase is a 45 kDa Zn2+-containing monomer. The larger 65 kDa L-fucose isomerase, which also acts on D-arabinose, is a hexameric Mn2+-dependent enzyme.1273 L-Arabinose isomerase of E. coli, which interconverts arabinose and L-ribulose, is a hexamer of 60-kDa subunits128 while the D-xylose isomerase of Streptomyces is a tetramer of 43-kDa subunits.129 The nonenzymatic counterpart of the isomerization catalyzed by the enzyme is the base-catalyzed Lobry deBruyn-Alberda van Ekenstein transformation (Eq. 13-25).130... 

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