Ribose 5-pyrophosphate

Fig. 15. pH dependence of the pKp values of lactate dehydrogenase complexes with (a) NADH, ( >) dihydronicotinamide-benzimidazole dinucleotide, (c) dihydronicotinamide-ribose-5 -pyrophosphate-5"-ribose... 

D-Ribose 5-pyrophosphate hcis been S5mthesized by treating D-ribose 5-phosphate with dicyclohexylcarbodiimide and inorganic phosphate . 

Synthetic cytidine ribitol pyrophosphate was prepared by condensing cytidine 5-phosphate and D-ribose 5-phosphate in the presence of dicyclohexylcarbodiimide, followed by the reduction of the cytidine D-ribose pyrophosphate with sodium borohydride. 

The reaction of [Cp Rh(H2O)3](OT02 with nicotine adenine dinucleotide (NAD ) afforded the cyclic trimer structure, [Cp Rh - VN 1 ) (N6,N7)-9-(5 -ribose pyrophosphate-5"-ribose-T-nicotinamide)adeninato ]3(OTf)3 162, which was fully characterized. ... 

Fig. 3.6. The a-specificity of the alcohol dehydrogenase as demonstrated by using deuterium labelled alcohol as substrate and then recovering the deuterium by the reverse reaction. D, deuterium R, ribose-pyrophosphate-ribose-adenine moiety of NAD (see Fig. 4.6).

The pathways for thiamine biosynthesis have been elucidated only partiy. Thiamine pyrophosphate is made universally from the precursors 4-amino-5-hydroxymethyl-2-methylpytimidinepyrophosphate [841-01-0] (47) and 4-methyl-5-(2-hydroxyethyl)thiazolephosphate [3269-79-2] (48), but there appear to be different pathways ia the eadier steps. In bacteria, the early steps of the pyrimidine biosynthesis are same as those of purine nucleotide biosynthesis, 5-Aminoimidazole ribotide [41535-66-4] (AIR) (49) appears to be the sole and last common iatermediate ultimately the elements are suppHed by glycine, formate, and ribose. AIR is rearranged in a complex manner to the pyrimidine by an as-yet undetermined mechanism. In yeasts, the pathway to the pyrimidine is less well understood and maybe different (74—83) (Fig. 9). 

The TK-catalyzed reaction requires the presence of thiamine pyrophosphate and Mg " as cofactors. Although the substrate specificity of the enzyme has not been thoroughly investigated, it has been shown that the enzyme accepts a wide variety of 2-hydroxyaldehydes including D-glyceraldehyde 3-phosphate [591-57-1], D-glyceraldehyde [453-17-8], D-ribose 5-phosphate /47(9(9-2%/7, D-erythrose 4-phosphate and D-erythrose [583-50-6] (139,149—151). 

Nicotinamide adenine dinucleotide (NAD) Fructose 1,6-diphosphate Glucose-6-phosphate Isopentenyl pyrophosphate Ribose-6-phosphate-l-pyrophosphate... 

There are basically two types of salvage. The first involves attachment of the base to PRPP with the formation of pyrophosphate. This pathway is available for salvage of purines and uracil but not for cytosine or thymine. The other pathway involves attachment of the base to ribose 1-phosphate, which occurs to some extent for most of the purines and pyrimidines. This second pathway requires the presence of specific... 

A different, simpler , pathway is involved in the synthesis of pyrimidine nucleotides. A pyrimidine base (orotate), is synthesised first. Then the ribose is added from 5-phosphoribosyl 1-pyrophosphate. The two precursors for the formation of orotate are carbamoylphosphate and aspartate, which form carbamoyl aspartate, catalysed by aspartate carbamoyltransferase. 

Figure 20.9 The positions in the pathway for de novo pyrimidine nucleotide synthesis where GLUCOSE provides the ribose molecule and GLUTAMINE provides nitrogen atoms. Glucose forms ribose 5-phosphate, via the pentose phosphate pathway (see chapter 6), which enters the pathway, after phosphorylation, as 5-phospho-ribosyl 1-pyrophosphate. Glutamine provides the nitrogen atom to synthesise carbamoylphos-phate (with formation of glutamate), and also to form cytidine triphosphate (CTP) from uridine triphosphate (UTP), catalysed by the enzyme CTP synthetase. It is the amide nitrogen of glutamine that is the nitrogen atom that is provided in these reactions.

The first step of this sequence, which is not unique to de novo purine nucleotide biosynthesis, is the synthesis of 5-phosphoribosylpyrophosphate (PRPP) from ribose-5-phosphate and adenosine triphosphate. Phosphoribosyl-pyrophosphate synthetase, the enzyme that catalyses this reaction [278], is under feedback control by adenosine triphosphate [279]. Cordycepin interferes with thede novo pathway [229, 280, 281), and cordycepin triphosphate inhibits the synthesis of PRPP in extracts from Ehrlich ascites tumour cells [282]. Formycin [283], probably as the triphosphate, 9-0-D-xylofuranosyladenine [157] triphosphate, and decoyinine (LXXlll) [284-286] (p. 89) also inhibit the synthesis of PRPP in tumour cells, and this is held to be the blockade most important to their cytotoxic action. It has been suggested but not established that tubercidin (triphosphate) may also be an inhibitor of this reaction [193]. 

In standard conditions, the change in free enthalpy AG° (see p. 18) that occurs in the hydrolysis of phosphoric acid anhydride bonds amounts to -30 to -35 kj mol at pH 7. The particular anhydride bond of ATP that is cleaved only has a minor influence on AG° (1-2). Even the hydrolysis of diphosphate (also known as pyrophosphate 4) still yields more than -30 kJ mol . By contrast, cleavage of the ester bond between ribose and phosphate only provides -9 kJ mol (3). 

This enzyme [EC 2.4.2.7], also referred to as AMP pyro-phosphorylase and transphosphoribosidase, catalyzes the reaction of AMP and pyrophosphate (or, diphosphate) to generate adenine and 5-phospho-a-ribose 1-diphosphate. In the reverse reaction, 5-amino-4-imidaz-olecarboxyamide can replace adenine. 

This enzyme [EC 2.4.2.17], also known as phosphoribo-syl-ATP pyrophosphorylase, catalyzes the reaction of ATP with 5-phospho-a-D-ribose 1-diphosphate to generate l-(5-phospho-D-ribosyl)-ATP and pyrophosphate. 

This enzyme [EC 2.4.2.19], also referred to as nicotinate mononucleotide pyrophosphorylase (carboxylating), catalyzes the reversible reaction of pyridine 2,3-dicar-boxylate and 5-phospho-a-o-ribose 1-diphosphate to produce nicotinate D-ribonucleotide, carbon dioxide, and pyrophosphate. 

This thiamin pyrophosphate-dependent enzyme [EC 2.2.1.1], also known as glycolaldehyde transferase, catalyzes the reversible reaction of sedoheptulose 7-phos-phate with D-glyceraldehyde 3-phosphate to produce D-ribose 5-phosphate and o-xylulose 5-phosphate. The enzyme exhibits a wide specificity for both reactants. It also can catalyze the reaction of hydroxypyruvate with R—CHO to produce carbon dioxide and R—CH(OH)—C(=0)—CH2OH. Transketolase isolated from Alkaligenes faecalis shows high activity with D-erythrose as the acceptor substrate. 

If the terminal pyrophosphate is removed from a molecule of ATP, the remainder is AMP, adenosine monophosphate, one of the four building blocks of the important biological macromolecules, the nucleic acids. There are two types of nucleic acids (26) ribonucleic acid (RNA), and deoxyribonucleic acid (DNA). RNA is a polymer of four different nucleotides, one of which is AMP, the ribose phosphate of adenine. The other three nucleotides are also ribose phosphates of heterocyclic bases, guanine, cytosine, and uracil. The structure of the four bases is shown in Figure 6. 

Attack at the /3 phosphate of ATP displaces AMP and transfers a pyrophosphoiyl (not pyrophosphate) group to the attacking nucleophile (Pig. 13-10b). For example, the formation of 5 -phosphoribosyl-1-pyrophosphate (p. XXX), a key intermediate in nucleotide synthesis, results from attack of an —OH of the ribose on the /3 phosphate. 

Phosphoribosyl pyrophosphate (PRPP) is important in both, and in these pathways the structure of ribose is retained in the product nucleotide, in contrast to its fate in the tryptophan and histidine biosynthetic pathways discussed earlier. An amino acid is an important precursor in each type of pathway glycine for purines and aspartate for pyrimidines. Glutamine again is the most important source of amino groups—in five different steps in the de novo pathways. Aspartate is also used as the source of an amino group in the purine pathways, in two steps. 

Vitamin Bt Thiamine Thiamine pyrophosphate Y Cofactor of enzymes catalyzing Pyruvate -> acetyl CoA a-Ketoglutarate -> Succinyl CoA RiboseS-P xylulose S-P -> Sedoheptulose 7-P + Glyceraldehyde 3-P... 

During the conversion of anthranilate to tryptophan, two additional carbon atoms must be incorporated to form the indole ring. These are derived from phosphoribosyl pyrophosphate (PRPP) which is formed from ribose 5-phosphate by transfer of a pyro-phospho group from ATP.60 61 The - OH group on the anomeric carbon of the ribose phosphate displaces AMP by attack on Pp of ATP (Eq. 25-5). In many organisms the enzyme that catalyzes this reaction is fused to subunit II of anthranilate synthase.62 PRPP is also the donor of phosphoribosyl groups for biosynthesis of histidine (Fig. 25-13) and of nucleotides (Figs. 

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