5-Phosphoribosyl-l-pyrophosphate

Glutamine 5-phosphoribosyl-l-pyrophosphate amidotransferase, 38 310-311 Glutamine phosphoribosylpyrophosphate amidotransferase, ground spin state variability, 38 99-100 Glutathion... 

A useful way to organize these biosynthetic pathways is to group them into six families corresponding to their metabolic precursors (Table 22-1), and we use this approach to structure the detailed descriptions that follow. In addition to these six precursors, there is a notable intermediate in several pathways of amino acid and nucleotide synthesis—5-phosphoribosyl-l-pyrophosphate (PRPP) ... 

Recently, the formation of a covalent glycosyl-enzyme intermediate was also shown by Bell and Koshland (17) in another reaction. Evidence was presented that the mechanism of the enzyme, phosphoribosyl-adeno-sine triphosphate pyrophosphate phosphoribosyl transferase, proceeds through a covalent phosphoribosyl-enzyme intermediate. The intermediate has been demonstrated after incubating the enzyme with 14C-5-phosphoribosyl-l-pyrophosphate (PRPP) under native and denaturing conditions. The intermediate also forms from the reverse direction as shown when the enzyme is mixed with its product N- (5-phosphoribosyl-adenosine triphosphate (PR-ATP). These data give evidence for a covalent enzyme-substrate intermediate. The enzyme which catalyzes the overall reaction proceeds as follows ... 

Fe/S clusters in regulatory enzymes have been proposed to act as sensors in such a manner that, upon detection of a measurand, the cluster disintegrates and activity stops. Putative examples are NO sensing by the [2Fe-2S] cluster in the terminal enzyme of heme synthesis, ferrochelatase [8], and 02 sensing by the [4Fe-4S] cluster in the regulatory enzyme of purine nucleotide biosynthesis, glutamine 5-phosphoribosyl-l-pyrophosphate amidotransferase [9], This is of course not a catalytic activity, since the cluster is destroyed in the action. 

In the enzyme catalysis of the first committed step in the de novo synthesis of purines, an amino group from L-glutamine is transferred to 5-phosphoribosyl-l-pyrophosphate to form glutamate and 5-phosphoribosyl-1-amine. The assay includes glycinamide ribonucleotide synthetase, which converts 5-phosphoribosyl-l-amine to glycinamide ribonucleotide, which is the reaction product quantitated. 

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. 

Phosphoribosyl-l-pyrophosphate (PRPP) synthesis is catalyzed by PRPP synthetase. Note the ribose-5-phosphate for the pathway comes from tlie Pentose Phosphate Pathway (see "PPP/Gluconeogenesis" Lecture). 

Phosphoribosyl-l -pyrophosphate (PRPP), which provides the ribose moiety, reacts with glutamine to form phosphoribosylamine. 

In December 1988, the company introduced a new strain of B. amyloliquefaciens (strain V), which had been genetically modified to increase the synthesis of 5-phosphoribosyl-l-pyrophosphate, an intermediate in the biosynthesis of tryptophan (see Figure 1). After fermentation, tryptophan was extracted from the broth and purified using a series of filtration, crystallization, and separation processes. The purification procedures included contact with powdered activated carbon and then granulated activated carbon. The amount of powdered activated carbon in each batch was usually... 

Phosphoribosyl-l-pyrophosphate (PRPP) is a key intermediate in nucleotide biosynthesis. It is required for de novo synthesis of purine and pyrimidine nucleotides and the salvage pathways, in which purines are converted to their respective nucleotides via transfer of ribose 1-phosphate group from PRPP to the base that is. 

The branch starting with anthranilate leads to the synthesis of trypto phan (Figure 24.15). Chorismate acquires an amino group derived from the hydrolysis of the side chain of glutamine and releases pyruvate to forin anthranilate. Then anthranilate condenses with 5-phosphoribosyl-l-pyrophosphate (PRPP), an activated form of ribose phosphate. PRPP is also... 

A11 diseases are autosomal recessive unless otherwise indicated. AD, autosomal dominant XLR, X-linked recessive PRPP, 5-phosphoribosyl-l-pyrophosphate HGPRT, hypoxanthine-guanine phosphoribosyl-transferase. 

The answer is c. (Ivlurray, pp 375— /O I. Scrivt i, pp 2513—2570. Sack, pp 121—138. Wilson, pp 287—320.1 Several control sites exist in the path of purine synthesis where feedback inhibition occurs, AMP, GMP, or IMP may inhibit the first step of the pathway, which is the synthesis ol 5-phosphoribosyl-l-pyrophosphate (PRPP). PRPP synthetase is specifically inhibited. All three nucleotides can inhibit glutamine PRPP aminotranslerase, which catalyzes the second step of the. pathway. AMP blocks the conversion ol IMP to adenylosuccinate. GMP inhibits the lormation ol xanthylate Irom IMP Thus, blockage rather than enhancement ol IMP metabolism to AMP and GMP effectively inhibits purine biosynthesis. 

The answer is c, (Murray, pp 375-801. Scriver, pp 2513-2570. Sack, pp 121-138. Wilson, pp 287-320.) 5 -phosphoribosyl-l-pyrophosphate (PRPP) donates the ribose phosphate unit of nucleotides and is absolutely required for the beginning of the synthesis of purines. In fact, the enzymes regulating the synthesis of PRPP and the subsequent synthesis of phospho-ribosylamine from PRPP are all end product-inhibited by inosine... 

The answer is a. (Murray, pp 627-661. Scriver, pp 3897-3964. Sack, pp 121—138. Wilson, pp 287-320.) The major contributor of electrons in reductive biosynthetic reactions is nicotinamide adenine dinucleotide phosphate (NADPH -I- H ), which is derived by reduction of NAD. NAD is formed from the vitamin niacin (also called nicotinate). Niacin can be formed from tryptophan in humans. In the synthesis of NAD, niacin reacts with 5-phosphoribosyl-l-pyrophosphate to form nicotinate ribonucleotide. Then, AMP is transferred from ATP to nicotinate ribonucleotide. Finally, the amide group of glutamate is transferred to the niacin carboxyl group to form the final product, NAD. NADP is derived from NAD by phosphorylation of the 2 -hydroxyl group of the adenine ribose moiety. The reduction of NADP to NADPH -I- H occurs primarily through the hexose monophosphate shunt. 

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

Fluorouracil (5-FU) requires enzymatic conversion to the nucleotide (ribosylation and phosphorylation) in order to exert its cytotoxic activity. Several routes are available for the formation of floxuridine monophosphate (FUMP). 5-FU may be converted to fluorouridine by uridine phos-phorylase and then to FUMP by uridine kinase, or it may react directly with 5-phosphoribosyl-l-pyrophosphate (PRPP), in a reaction catalyzed by orotate phosphoribosyl transferase, to form FUMP. Many metabolic pathways are available to FUMP. As the triphosphate FUTP, it may be incorporated into RNA. An alternative reaction sequence... 

Ribose-5-phosphate is an intermediate in the Calvin cycle and in synthesis of 5-phosphoribosyl-l-pyrophosphate, an intermediate in nucleotide biosynthesis. 

Purine salvage usually involves phosphoribosyltransferase reactions, which generate ribonucleoside monophosphates (rNMPs) from the purine bases and 5-phosphoribosyl-l-pyrophosphate (PRPP). These are phosphorylated to diphosphates (rNDPs) and then reduced to deoxyribonucleotides (dNDPs) with ribonucleotide reductase. 

As purines are built on a ribose base (see Fig. 41.2), an activated form of ribose is used to initiate the purine biosynthetic pathway. 5-Phosphoribosyl-l-pyrophosphate (PRPP) is the activated source of the ribose moiety. It is synthesized from ATP and ribose 5 -phosphate (Fig. 41.3), which is produced from glucose through the pentose phosphate pathway (see Chapter 29). The enzyme that catalyzes this reaction, PRPP synthetase, is a regulated enzyme (see section 1I.A.5) however, this step is not the committed step of purine biosynthesis. PRPP has many other uses, which are described as the chapter progresses. 

Which of the following statements about 5-phosphoribosyl-l-pyrophosphate (PRPP) are true ... 

The first step in de novo pyrimidine biosynthesis is the synthesis of carbamoyl phosphate from bicarbonate and ammonia in a multistep process, requiring the cleavage of two molecules of ATP. This reaction is catalyzed by carbamoyl phosphate synthetase (CPS), and the bicarbonate is phosphorylated by ATP to form carboxyphosphate and ADP (adenine dinucleotide phosphate). Ammonia then reacts with carboxyphosphate to form carbamic acid. The latter is phosphorylated by another molecule of ATP with the mediation of CPS to form carbamoyl phosphate, which reacts with aspartate by aspartate transcarbamoy-lase to form A-carbamoylaspartate. The latter cyclizes to form dihydroorotate, which is then oxidized by NAD-1- to generate orotate. Reaction of orotate with 5-phosphoribosyl-l-pyrophosphate (PRPP), catalyzed by pyrimidine PT, forms the pyrimidine nucleotide orotidylate. This reaction is driven by the hydrolysis of pyrophosphate. Decarboxylatin of orotidylate, catalyzed by orotidylate decarboxylase, forms uridylate (uridine-5 -monophosphate, UMP), a major pyrimidine nucleotide that is a precursor of RNA (Figure 6.53). 

An important compound in biochemistry is 5-phosphoribosyl-l-pyrophosphate (PRPP) (10.13). This compound is involved in the biosynthesis of amino acids and NAD (Chapter 11.5). 

Enzymes which catalyse the transfer of a pyrophosphate group are sometimes known as pyrophosphorylases. Although ATP normally functions as a phosphorylating agent, it will sometimes act as a pyrophosphorylating agent, as, for example, in the conversion of ribose-5-phosphate into a-5-phosphoribosyl-l-pyrophosphate (PRPP). 

The 5 phosphoribosyl-l-pyrophosphate required for purine synthesis is obtained from ATP and ribose-5-phosphate by reaction (11.39). Glutamine, which is also required, is obtained from glutamic acid by reaction (11.44), and the latter is obtained from a - oxoglutaric acid by reaction (11.124). The last reaction links the Krebs cycle with amino acid metabolism. 

The elucidation of the last steps of pyrimidine synthesis de novo came from the study of Hurlbert and Potter [107] which showed that uridine nucleotides were intermediates in the conversion of orotate to pyrimidines of nucleic acids. UMP was the first of the three uridine 5 -phosphates to become labelled in this process [108]. The synthesis of UMP from orotate takes place in two steps the stoichiometric condensation [109] of orotic acid with 5-phosphoribosyl-l-pyrophosphate (PRPP) to form orotidine 5 -phosphate and its subsequent irreversible decarboxylation to UMP ... 

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