Ribosyl phosphate

Phosphoglucomutase acts not only on D-glucose and D-mannose phosphates (see p. 204) but also on D-ribose phosphates, the interconversion of D-ribosyl phosphate and D-ribose 5-phosphate being similarly accelerated by D-glucose 1,6-diphosphate,193 which appears to generate D-ribose 1,5-diphos-phate as cofactor.199(a) (b) (o) D-Ribose 5-phosphate is formed from D-ribose and ATP in the presence of yeast ribokinase.m... 

Deoxy-D-ribose 5-phosphate 2-deoxy-D-ribosyl phosphate (1)... 

Deoxy-a-D-ribosyl-l-phosphate 20, a key substrate in the preparation of 2 -deoxynucleosides, was stereoselectively prepared by crystallization-induced asymmetric transformation in the presence of an excess of ortho-phosphoric acid and tri( -butyl)amine under strictly anhydrous conditions (Scheme 2).7 Initial Sn2 displacement of Cl in ot-glycosyl chloride 16 by phosphoric acid resulted in a 1 1 a/p anomeric mixture of 17 and 18 due to the rapid anomerisation of the a-chloride in polar solvents. Under acidic conditions, in the presence of an excess of H3P04, an equilibration between the a and p anomers gradually changed in favour of the thermodynamically more stable a-counterpart. By selective crystallization of the mono tri( -butyl)ammonium salt of the a-phosphate from the mixture, the equilibrium could be shifted towards the desired a-D-ribosyl phosphate 18 (oc/p = 98.5 1.5), which was isolated as bis-cyclohexylammonium salt 19 and deprotected to furnish compound 20. 

Lampen (see Ref. 56) had prepared a 1-D-ribosylthymine from thymine plus D-ribosyl phosphate in the presence of nucleosidases from Escherichia coli B. 

A phosphorylase from Escherichia coli has been purified it is specific for 2-deoxy-D-ribosyl phosphate, but can use uracil, 2-thiouracil, 5-amino-uracil, 5-bromouracil, and 2-thiothymine as a pyrimidine. Deaminases of adenosine, 2-deoxyadenosine, cytidine, and 2-deoxycytidine have been detected in Escherichia coli. 

The transformation of precursors into NAD (56) and NADP (57) follow the same pathway in all organisms. A ribosyl phosphate residue can be transferred to biosynthetic quinolinic acid... 

Small amounts of purine ribonucleosides and deoxyribo -nucleosides can be prepared enzymically. Two types of enzyme have been found that catalyze the synthesis of nucleosides. The first are the nucleoside phos-phorylases, which catalyze the reaction of purines and D-ribosyl phosphate or 2-deoxy- D-ribosyl phosphate as follows. 

Guanine + D-ribosyl phosphate guanosine -f- phosphate Hypoxanthine + D-ribosyl phosphate inosine + phosphate Hypoxanthine 2-deoxy- D-ribosyl phosphate 2-deoxyinosine + phosphate... 

The D-ribosyl phosphate formed by the reverse reaction pictured above has been shown to be a-D-ribofuranosyl phosphate, so that the reaction proceeds, in either direction, with an inversion of anomerie configuration, as does the condensation reaction of heavy-metal salts of purines with acylglycosyl halides. Although the anomerie configuration of 2-deoxy- D-ribofuranosyl phosphate has not been determined, it presumably is also a. 

NOTE 4 These enzymes (2.4.2.1 - 2.4.2.23) generally catalyze the reactions Purine or pyrimidine nucleoside + orthophosphate or pyrophosphate = purine or pyrimidine + a ribose or ribosyl phosphate, ribosyl diphosphate, or ribosyl pyrophosphate.]... 

It is as nucleotides, i.e., ribosyl phosphate derivatives, that most of the reactions of purines and pyrimidines take place, and the origin of the ribosyl phosphate moiety must therefore be discussed. The deoxyribosyl phosphate moiety of deoxyribonucleotides is synthesized by way of ribonucleotides, and this process will be discussed in Chapter 16. The pertinent literature through 1962 has been reviewed in the English edition of Hollman s book (I) references given there will not usually be repeated here. 

Purine bases can be converted to ribonucleotides via phosphoribosyl-transferases PP-ribose-P provides the ribosyl phosphate moiety. Purine nucleosides can be phosphorylated by ATP-requiring nucleoside kinases to form the same ribonucleotides. Finally, the possibility also exists that purine bases are first converted to ribonucleosides via nucleoside phos-phorylase, and then to ribonucleotides by the above-mentioned kinases. These routes of ribonucleotide synthesis are summarized as follows ... 

The intermediate, compound III, is of major significance in the proposed sequence in histidine biosynthesis. Although it has not been identified, it is presumed to be iV-l-ribosyl phosphate adenosinyl triphosphate. 

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