Phosphates sugar

In deoxy sugars, one or more hydroxyl groups of the pyranose or furanose ring is substituted by hydrogen. A well-known example is 2-deoxyribose, which is a component of deoxyribonucleotides, the repeating units of deoxyribonucleic acids (DNA). Another example is L-fucose 

2-Deoxy- D-ribose-5-phosphate (2-cieoxy-D-ribofuranosyl-5-phosphate) 

Sugar phosphates and a nucleoside diphosphate sugar. When the anomeric position of a sugar is not substituted, the configuration at this position is not specified because the sugar can exist in either the a- or j6-anomeric form. 

These two deoxy sugars are the rare monosaccharides that are in the u-configuration. u-Rhamnose is a constituent of lipopolysaccharides of the outer membrane layer of gram-negative bacteria. L-Fucose is a constituent of glycoproteins in cell membranes. 

L-Fucose occurs either at terminal or preterminal positions of many cell surface oligosaccharide ligands. These fucosylated oligosaccharides mediate cell-cell recognition and adhesion-signaling pathways. Some of these processes 

The sugar phosphates are separated on ECTEOLA-cellulose thin-layers impregnated with ammonium tetraborate (see section II, 6) with solvent XXV [11]. The mobility of the sugars is altered by preparing the solvent and plates with pH 10 ammonium tetraborate buffer. Table 207 gives the mobilities of some common sugar phosphates. 

For visualization of the sugar phosphates, the plates are sprayed successively with benzidine tricMoroacetate (Rgt. No. 21) to detect the hexose 6-phosphates, and with the molybdate reagent (Rgt. No. 166) which detects all phosphates. The lower limits of detection of the two reagents are 10 and 5 [x moles, respectively. Stannous chloride reagent also reveals the sugar phosphates. 

The structures of keto-sugars in solution, together with those of their biologically important phosphate esters, have been reviewed, and rapid-quench kinetic experi- 

Rat liver plasma membranes contain an enzyme that can catalyse the formation of alkyl esters of adenosine 5 -phosphate, e.g. (14 R=CH2CH20H) or (14 R = Me), from ATP and the corresponding alcohol. The concentration of alcohol must be high for the syntheses to proceed at an appreciable rate, and hence (14) may be formed as a result of the diversion of some other metabolic pathway. 

The syntheses of various glycosyl phosphates have been described in detail, as has the phosphorylation of 5,6-O-isopropylidene-L-ascorbic 

Oxidation of D-glucuronic acid 6-phosphate by vanadium pentoxide and chlorate ion gives D-ara.-hex-2-ulosonic acid 6-phosphate (56), which is a known intermediate in carbohydrate metabolism. In the presence of alkali, (56) is unstable and breaks down by a retro-aldol reaction to a triose phosphate. 

Nomura, M. Shimomura, and S. Morimoto, Chem. and Pharm. Bull. Japan), 1971, 19, 1433. 

The syntheses of sucrose 6 -phosphate, methyl a-mannopyranoside 4- and 6-phosphates, and 3-deoxy-3-fluoro-D-glucose 1- and 6-phosphates [ (57) and (58) ] have been described. Neither (57) nor (58) was a substrate for UDPGlc-pyrophosphorylase or phosphoglucomutase, although (58) was a poor substrate for glucose 6-phosphate dehydrogenase.  

Phosphate esters of monosaccharides are found in all hving cells, where they are intermediates in carbohydrate metabolism. Some common sugar phosphates are the following  

Phosphates of the five-carbon sugar ribose and its 2-deoxy analog are important in nucleic acid structures (DNA and RNA) and in other key biological compounds (Sec. 18.12). 

Synthesis.—Comprehensive reviews on glycosyl esters of nucleoside pyrc -phosphates and teichoic acids have appeared in the past year as have details of the preparation of xylulose-5-phosphate using transketolase. Phosphorylation of glucose by inorganic phosphate in the presence of histidine occurs under simulated primitive earth conditions and the reactive species is probably an iST-phosphorylated histidine. Phosphorylation of sugars by heating them with 100% phosphoric acid in vacuo is a novel experimental 

Skeletal muscle and yeast phosphofructokinases will catalyse the phosphorylation of 5-keto-D-fructose-l,6-bisphosphate (9). The latter has been isolated chromatographically and identified by its phosphorus content and the rather doubtful method of acid lability of the phosphate groups. The bis-phosphate is a competitive inhibitor of the reaction between aldolases and fructose-1,6-bisphosphate probably because of Schiff base formation with the enzyme.  

Many of the simple trioses, tetroses, and pentoses do not occur naturally in the free state but are commonly found as phosphate-ester derivatives. The phospho-esters are important intermediates in the breakdown and synthesis of carbohydrates by living organisms. D-Glucose is converted into D-fructose-l,6-bisphos-phate that is then cleaved in half to give D-glyceraldehyde-3-phosphate and dihydroxy acetone phosphate (see Chapter 11). D-Erythrose is found as the 4-phosphate in the pentose-phosphate pathway of carbohydrate degradation and in the photosynthetic process. D-Ribose-5-phosphate, D-ribulose-5-phosphate, D-xy-lose-5-phosphate, and D-xylulose-5-phosphate are found in the pentose phosphate pathway as well as in the photosynthetic pathway (see Chapter 10). D-Ribulose-1,5-bisphosphate is the direct intermediate to which CO2 is added in the photosynthetic pathway. D-Ribose-5-phosphate also is the precursor of RNA (ribonucleic acid) and DNA (deoxyribonucleic acid). See Fig. 1.7 for the structures of these common sugar phosphates. 

In addition to the naturally occurring deoxy, amino, and phospho sugars, other kinds of esters, ethers, and substituted carbohydrates (carbohydrates with hydroxyl and/or hydrogen replaced by other groups), can be chemically or enzymatically synthesized (see Chapter 4). 

3-Deoxy-araWno-heptulosonic acid 7-phosphate (10) is a metabolic intermediate before shikimic acid in the biosynthetic pathway to aromatic amino-acids in bacteria and plants. While (10) is formed enzymically from erythrose 4-phosphate (11) and phosphoenol pyruvate, a one-step chemical synthesis from (11) and oxalacetate has now been published.36 The synthesis takes place at room temperature and neutral pH 

1-phosphate 6-sulphate, which is a substrate for both aldolase and fructose 1,6-bisphosphatase.40 The anomeric composition of (15) as determined by 31P n.m.r. was 20 %a and 80%/ , a value which corresponds closely to that obtained by 13C n.m.r. for fructose 1,6-bisphosphate.41 

The enthalpies of hydrolysis of glycoside cyclic phosphodiesters have been measured42 by flow microcalorimetry, using a phosphohydrolase from Enterobacter aerogenesiz as catalyst. This phosphohydrolase can hydrolyse a wide variety of phosphodiesters, which enables the enthalpies of hydrolysis of glycoside cyclic phosphodiesters to be compared with those of acyclic and monocyclic phosphodiesters. It was found42 that the phosphohydrolase cleaves the 3 - and 5 -ester bonds with similar enthalpies, which are less negative (—11.1 0.2 kcal mol-1) than the value (-13.2 0.4 kcal mol-1) that had been reported previously.44 

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As shown in Figure 45.1, the bases appear in complementary pairs, A with T and G with C in this particular example, the sequence for one strand of DNA is A-T-C-G-T- while the other strand is -T-A-G-C-A-. The sequences of the bases attached to the sugar-phosphate backbone direct the production of proteins from amino acids. Along each strand, groups of three bases, called codons, correspond to individual amino acids. For example, in Figure 45.1, the triplet CGT, acting as a codon, would correspond to the amino acid serine. One codon, TAG, indicates where synthesis should begin in the DNA strand, and other codons, such as ATT, indicate where synthesis should stop. 

Polymerization of nucleotides occurs through the sugar and phosphate groups so that the polymers consist of a sugar-phosphate backbone having pendent bases. 

Figure 7.1 Schematic drawing of B-DNA. Each atom of the sugar-phosphate backbones of the double helix is represented as connected circles within ribbons. The two sugar-phosphate backbones are highlighted by orange ribbons. The base pairs that are connected to the backbone are represented as blue planks.

Figure 7.2 Three helical forms of DNA, each containing 22 nucleotide pairs, shown in both side and top views. The sugar-phosphate backbone is dark the paired nucleotide bases are light, (a) B-DNA, which is the most common form in cells, (b) A-DNA, which is obtained under dehydrated nonphysiological conditions. Notice the hole along the helical axis in this form, (c) Z-DNA, which can be formed by certain DNA sequences under special circumstances. (Courtesy of Richard Feldmann.)...

Figure 7.4 The edges of the base pairs in DNA that ate in the major groove are wider than those in the minor groove, due to the asymmetric-attachment of the base pairs to the sugar-phosphate backbone (a). These edges contain different hydrogen bond donors and acceptors for potentially specific interactions with proteins (b).

The sugar-phosphate backbone is represented by connected circles in color and the base pairs as blue planks. Four base pairs are shown from the top of the helix to highlight how the grooves are formed due to the asymmetric connections. The position of the helix axis is marked by a cross. 

The binding model, suggested by Brian Matthews, is shown schematically in (a) with connected circles for the Ca positions, (b) A schematic diagram of the Cro dimer with different colors for the two subunits, (c) A schematic space-filling model of the dimer of Cro bound to a bent B-DNA molecule. The sugar-phosphate backbone of DNA is orange, and the bases ate yellow. Protein atoms are colored red, blue, green, and white, [(a) Adapted from D. Ohlendorf et al., /. Mol. Evol. 19 109-114, 1983. (c) Courtesy of Brian Matthews.]... 

H-bonds between sugar-phosphate backbone and protein help anchor protein to DNA... 

Figure 3.13 shows the thermal stability of immobilized ODN and PNA. The signal for the Thy- and Cyt-bases obtained with temperature-programmed (TP) SIMS starts to decrease at approximately 150 °C for ODN and 200 °C for PNA. This variance is caused by the different strengths of binding between the bases and the sugar-phosphate and peptide backbones, respectively. 

RNA is relatively resistant to the effects of dilute acid, but gentle treatment of DNA with 1 mM HCl leads to hydrolysis of purine glycosidic bonds and the loss of purine bases from the DNA. The glycosidic bonds between pyrimidine bases and 2 -deoxyribose are not affected, and, in this case, the polynucleotide s sugar-phosphate backbone remains intact. The purine-free polynucleotide product is called apurinic acid. 

The base-specific chemical cleavage (or Maxam-Gilbert) method starts with a single-stranded DNA that is labeled at one end with radioactive (Double-stranded DNA can be used if only one strand is labeled at only one of its ends.) The DNA strand is then randomly cleaved by reactions that specifically fragment its sugar-phosphate backbone only where certain bases have been chemically removed. There is no unique reaction for each of the four bases. However,... 

A stereochemical consequence of the way A T and G C base pairs form is that the sugars of the respective nucleotides have opposite orientations, and thus the sugar-phosphate backbones of the two chains run in opposite or... 

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