Of D-ribose 5-phosphate

The above transketolase and transaldolase reactions were found inadequate to explain the metabolism of D-ribose 5-phosphate, because of the non-accumulation of tetrose phosphate, the 75 % yield of hexose phosphate, and the results of experiments with C14 (the distribution of which differed markedly from the values predicted for such a sequence). 24(b) Thus, with D-ribose-l-C14, using rat-liver enzymes, any hexose formed should have equal radioactivity at Cl and C3, whereas, actually, 74% appeared at Cl. Furthermore, D-ribose-2,3-Cl42 should have given material having equal labels at C2 and C4 in the resultant hexose, whereas, in fact, it had 50% of the activity at C4, C3 was nearly as active as C2, and Cl had little activity. Similar results were obtained with pea-leaf and -root preparations.24 The following reactions, for which there is enzymic evidence,170(b) were proposed, in addition to those involving D-aftro-heptulose, to account for these results.24(b) (o) 200... 

Hampton, A., Perini, F., and Harper, P.J., Derivatives of phosphonate and vinyl phosphate analogs of D-ribose 5-phosphate, Carbohydr. Res., 37, 359,... 

The reaction catalyzed by KDO 8-phosphate synthetase (reaction 2, Scheme 35) was first observed by Levin and Racker9 in extracts from Pseudomonas aeruginosa (see Scheme 1), and later by Ghalambor and Heath29 in extracts from Escherichia coli 0111 B4 and J-5. In the initial experiments of Levin and Racker,135 the fate of D-ribose 5-phosphate in crude bacterial extracts was studied, and the KDO 8-phosphate discovered by the authors is really derived from D-ribose 5-phosphate by three, sequential, enzyme-catalyzed reactions (see Scheme 36). 

It has been noted that, in the radiolysis of D-ribose 5-phosphate in D20, where the radicals 6 or 7, or both, are generated, free radical or substrate reduction, or both, mainly leads to incorporation of H at C-5 of the product, 5-deoxy-D-eryfhro-pentos-4-ulose, probably by way of transfer of a carbon-bound, hydrogen atom87 (compare Sect. Ill,3a). 

Scheme 12.—Dephosphorylation Reactions Starting from the Radicals at C-5 and C-3 of D-Ribose 5-Phosphate.

Scheme 13.—Mechanism Proposed for the Decay of the Peroxyl Radical at C-5 of d-Ribose 5-Phosphate.

Phosphorylation of XLVII with phosphorus oxychloride in pyridine solution, followed by hydrolysis to remove the methyl and isopropylidene residues, gave D-ribose 5-phosphate (XLVIII) which, as its barium salt, was found to be identical with the barium salt of the D-ribose phosphate from inosinic acid. By way of further confirmation of the structure of D-ribose 5-phosphate, Levene, Harris and Stiller129 showed that in methanolic hydrogen chloride solution both the natural and synthetic material mutarotated in a manner characteristic of a sugar which can form only a furanoside. 

The synthesis of D-ribose 5-phosphate has recently been markedly improved by Michelson and Todd127 through the use of dibenzylchloro-phosphonate as a phosphorylating agent. Methyl 2,3-isopropylidene-D-... 

In the first step, we showed by analytical studies that compound 28 was a donor substrate for transketolase in the presence of D-ribose-5-phosphate as acceptor substrate and that in the second step, the hydroxylated aldehyde released 29 led to the P-elimination of protected L-tyrosine. We showed that the free L-tyrosine can thus be obtained by enzymatic deprotection of N-acetyl-L-tyrosine ethyl ester using acylase and subtilisine. In this conditions, it should be possible to carry out this assay in vivo in the presence of host cells overexpressing transketolase and auxotrophic for L-tyrosin. This strategy should offer the first stereospecific selection test of transketolase mutants. The principle of this assay may be extended to other enzymes that can release aldehydes P-substituted by L-tyrosine. 

The reaction of D-ribose 5-phosphate with N-1 of adenosine 5-phosphate, followed by opening of the pyrimidine ring, has been implicated as part of the biosynthetic sequence to histidine. ... 

X-Ray irradiation of polycrystalline sodium and barium salts of D-glucose 1-and 6-phosphate and of D-ribose 5-phosphate produced P03 radicals, as evidenced by ESR spectroscopic studies no precursor phosphoranyl radicals were detected. ... 

Ribose-5-phosphate is the starting point of the pathway leading to purine synthesis. The first step which is the conversion of D-ribose-5-phosphate to 5-phospho-a-D-ribosyl pyrophosphate is catalysed by ribosephosphate pyrophos-phokinase. A later step involving condensation with glycine is catalysed by phos-... 

Condensation of D-ribose 5-phosphate with dihydroxy acetone phosphate under the influence of rabbit muscle aldolase gives D-gfycero-D-aftro-octulose which exists mainly in the pyranose ring form, and on treatment with triethylsilane is reduced to the C-glycoside 116, that is, a 2,6-anhydro-octitol. ... 

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