PRPP from ribose

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]. 

The formation of PRPP from ribose-5-phosphate and ATP is catalyzed by ribose-5-phosphate pyrophosphokinase (fig. 23.7). This is an unusual kinase because the pyrophos-phoryl group is transferred rather than the phosphoryl group. 

More energy is expended in route 1 (reactions 5.1 and 5.2) because ATP would be required to regenerate 5-phosphoribosepyrophosphate (PRPP) from ribose (reactions 5.4 and 5.5). PRPP is necessary for the biosynthesis of inosine in the uric acid cyde (Fig. 5.6). 

Phosphoribosylpyrophosphate (PRPP) synthetase (E.C. 2.7.6.1) catalyzes the formation of PRPP from ribose-5-phosphate and ATP in the presence of Mg and inorganic phosphate. The product, PRPP, is a substrate of the first rate limiting step of the de novo synthesis of purine nucleotides and its availability has been shown to regulate this pathway in human tissue (l). A superactive mutant erythrocyte PRPP synthetase with decreased sensitivity to feedback inhibition has recently been found by us in a gouty family (2,3). 

Tissues were homogenized in phosphate buffer and sonicated, and the supernatant was used for electrophoresis. Samples were run in phosphate buffer, pH 8.5, on cellulose acetate paper for 2 hours at 4 and at 0.5 mA/cm. PRPP synthetase was located on the paper by a radiochemical assay formation of PRPP from ribose-5-phosphate and ATP was coupled to inosinic acid (IMP) synthesis by the addition to the reaction mixture of labelled hypoxanthine and partially purified hypoxan-thine-guanine phosphoribosyltransferase (HGPRT). 

It was found that human as well as rabbit platelet lysates synthesize PRPP from ribose-5-phosphate and ATP. The average specific activities of PRPP synthetase in pooled human and pooled rabbit platelet lysates were 12 and 22 nmoles/mg protein/hr, respectively. 

The enzyme 5-phosphoribosyl-l-pyrophosphate (PRPP) synthetase (EC 2.7.6.l) catalyzes the synthesis of PRPP from ribose-5-phosphate (R-5-P) and adenosine 5 triphosphate (ATP) in the presence of magnesium and inorganic phosphate (9-ll). In the present communication we report studies on a mutant superactive PRPP synthetase in the erythrocytes of two brothers with excessive purine production associated with gout and uric acid lithiasis. In these two patients the serum uric acid reached 13.5 and 13.6 mg percent and the urinary 24 hours uric acid excretion 2400 mg and 2250 mg, respectively. All other members of the family examined were clinically and biochemically normal, except for the mother of the patients who had hyperuricosuria, 1100 mg per 24 hours. 

PRPP is synthesized from ribose 5-phosphate derived from the pentose phosphate pathway (see Fig. 14-21), in a reaction catalyzed by ribose phosphate pyro-phosphokinase ... 

PRPP is an "activated pentose" that participates in the synthesis of purines and pyrimidines, and in the salvage of purine bases (see p. 294). Synthesis of PRPP from ATP and ribose 5-phosphate is catalyzed by PRPP synthetase (ribose phosphate pyrophosphokinase, Figure 22.6). This enzyme is activated by inorganic phosphate (Pi) and inhibited by purine nucleotides (end-product inhibition). [Note The sugar moiety of PRPP is ribose, and therefore ribonucleotides are the end products of de novo purine synthesis. When deoxy-ribonucleotides are required for DNA synthesis, the ribose sugar moiety is reduced (see p. 295).]... 

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. 

At this stage, orotate couples to ribose, in the form of 5-phosphoribosyl-l-pyrophosphate (PRPP), a form of ribose activated to accept nucleotide bases. PRPP is synthesized from ribose-5-phosphate, formed by the pentose phosphate pathway, by the addition of pyrophosphate from ATP. Orotate reacts with PRPP to form orotidylate, a pyrimidine nucleotide. This reaction is driven by the hydrolysis of pyrophosphate. The enzyme that catalyzes this addition, pyrimidine phosphoribosyltransferase, is homologous to a number of other phosphoribosyltransferases that add different groups to PRPP to form the other nucleotides. Orotidylate is then decarboxylated to form uridylate (IMP), a major pyrimidine nucleotide that is a precursor to RNA. This reaction is catalyzed by orotidylate decarboxylase. 

Activated ribose phosphate. Write a balanced equation for the synthesis of PRPP from glucose through the oxidative branch of the pentose phosphate pathway. 

PRPP is synthesized from ribose 5-phosphate by the following reaction ... 

The source of the phosphoribosyl group of nucletotides is PRPP (5-phosphoribosyl-a-D-l-pyrophosphate). PRPP is generated from ribose-5-phosphate, a product of the pentose phosphate pathway. 

Figure 13-6. Coupled enzymatic synthesis of PRPP from D-ribose 351 i) ribokinase it) pyruvate kinase iii) PRPP-synthetase iv) adenylate kinase.

The precise energy requirement depends on how PRPP (phosphoribose pyrophosphate) is regenerated if, as shown above, it is regenerated from ribose, then a further 3ATPs are required, but if the PRPP is split from inosinic acid by pyiophosphorolysis, then no further ATP is required Reactions requiring ATP ... 

Histidine derives its carbon and nitrogen from ATP, ribose, and glutamine as indicated in Fig. 1. The pathway of histidine biosynthesis, as shown for bacteria and fungi, is given in Fig. 2 starting from ribose 5-phosphate and ATP. The first product, 5-phosphoribyosyl-1-pyrophosphate (PRPP), is also... 

Purines may also be derived from the nucleic acids present in animal and plant foods. After liberation in the course of digestion they are absorbed and react with PRPP from which they receive the ribose phosphate moiety. 

Phosphoribosyl-l-pyrophosphate (PRPP) may be considered a precursor in the de novo sjmthetic reactions of purines, since this ribose derivative was required for the formation of 5-phosphoribosylamine (PRA). PRA was the precursor of nitrogen 9, ribose, and phosphate of the completed purine nucleotide structure (Section II, B, 1). PRPP was also a key substance in the biosynthesis of pyrimidine nucleotides. This compound was formed from ribose 5-phosphate and ATP by a pyrophosphorylation of carbon 1 of ribose 5-phosphate (78-80). This was an unusual kinase reaction in that pyrophosphate was transferred rather than phosphate as was the case with most kinases. The ribose 5-phosphate required for the syntheas of PRPP probably originated from glucose, and was formed either by an oxidative pathway from glucose 6-phosphate via 6-pho hogluconate and ribulose 5-phosphate (81) or anaerobically from fructose 6-pho hate (88). The formation of PRPP is shown in Fig. 4. 

This important compound is formed from riboseS -phosphateand ATP by a kinase in mammalian and avian tissue, and in bacteria (S8-41) [Eq. (12)]. The pyrophosphate of PRPP is probably in the a-con6guration. The compound has been isolated and characterized (JS8-41), and has been chemically thesized (4 ). 

Phosphoribosylpyrophosphate (PRPP) synthetase is one of the very few enzymes which transfer a pyrophosphoryl group from ATP in one step. When the synthesis is carried out in lsO-enriched water, lsO is incorporated into the PRPP, but not into AMP.91 The lsO in the PRPP arises from a pre-exchange between the H2180 and the ribose phosphate, and hence the results confirm that fission of the /5-P—O bond takes place. PRPP and ATP are starting materials in the biosynthesis of histidine, and Ai-(5 -phospho-D-ribosyl)adenosine triphosphate (29) is an intermediate. The... 

Once orotate is formed, the ribose 5-phosphate side chain, provided once again by PRPP, is attached to yield orotidylate (Fig. 22-36). Orotidylate is then decarboxy-lated to uridylate, which is phosphorylated to UTP. CTP is formed from UTP by the action of cytidylate synthetase, by way of an acyl phosphate intermediate (consuming one ATP). The nitrogen donor is normally glutamine, although the cytidylate synthetases in many species can use NH4 directly. 

Purines that result from the normal turnover of cellular nucleic acids can be reconverted into nucleoside triphosphates and used by the body. Thus, they are "salvaged" instead of being degraded to uric acid. PRPP is the source of the ribose-phosphate, and the reactions are catalyzed by adenine phosphoribosyltransferase, and hypoxanthine-guanine phosphoribosyltransferase (HPRT). 

Figure 8.2. Synthesis of NAD from nicotinamide, nicotinic acid, and qninolinic acid. Quinolinate phosphoribosyltransferase, EC 2.4.2.19 nicotinic acid phosphoribosyl-transferase, EC 2.4.2.11 nicotinamide phosphoribosyltransferase, EC 2.4.2.12 nicotinamide deamidase, EC 3.5.1.19 NAD glycohydrolase, EC 3.2.2.S NAD pyrophosphatase, EC 3.6.1.22 ADP-ribosyltransferases, EC 2.4.2.31 and EC 2.4.2.36 and poly(ADP-ribose) polymerase, EC 2.4.2.30. PRPP, phosphoribosyl pyrophosphate.

Figure 25.1. Salvage and de Novo Pathways. In a salvage pathway, a base is reattached to a ribose, activated in the form of 5-phosphoribosyl-1-pyrophosphate (PRPP). In de novo synthesis, the base itself is synthesized from simpler starting materials, including amino acids. ATP hydrolysis is required for de novo synthesis.

Orotate Acquires a Ribose Ring from PRPP to Form a Pyrimidine Nucleotide and Is Converted into Uridylate... 

The pyrimidine ring is assembled first and then linked to ribose phosphate to form a pyrimidine nucleotide. PRPP is the donor of the ribose phosphate moiety. The synthesis of the pyrimidine ring starts with the formation of carbamoylaspartate from carbamoyl phosphate and aspartate, a reaction catalyzed by aspartate transcarbamoylase. Dehydration, cyclization, and oxidation yield orotate, which reacts with PRPP to give orotidylate. Decarboxylation of this pyrimidine nucleotide yields UMP. CTP is then formed by the amination of UTP. 

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