Purine synthesis <i>de novo</i> and its regulation in rat hepatocytes

Rosiers, Christine Des; Lalanne, Marcel; Willemot, J

doi:10.1139/o80-082

Cited by 14 publications

(5 citation statements)

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“…Therefore, although there was no strict correlation between glucose output and urate formation, it seems to be possible that the elevated level of glucose-6-phosphate caused an enhanced flux into the pentose phosphate pathway replenishing the 5-phosphoribosyl-l-pyrophosphate pool and in turn increasing purine nucleotide synthesis. This hypothesis is in agreement with the finding that glucagon, cAMP or adrenaline (noradrenaline was not tested) increased the levels of 5-phosphoribosyl-l-pyrophosphate in rat hepatocytes by 1.5-2-fold although with considerably slower kinetics [25,26]. The finding that adrenaline (noradrenaline was not studied) increased urate formation slightly by 1.2-1.5-fold in chicken hepatocytes again with considerably slower kinetics [27] cannot be compared with the present observations since in birds urate is the end product not only of the degradation of purine nucleotides as in mammals but of all nitrogenous compounds including amino acids.…”

Section: Discussionsupporting

confidence: 91%

Increase of urate formation by stimulation of sympathetic hepatic nerves, circulating noradrenaline and glucagon in the perfused rat liver

1987

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In the isolated rat liver perfused in situ stimulation of the nerve bundles around the portal vein and the hepatic artery caused an increase of urate formation that was inhibited by the cq-blocker prazosine and the xanthine oxidase inhibitor allopurinol. Moreover, nerve stimulation increased glucose and lactate output and decreased perfusion flow. Infusion of noradrenaline had similar effects. Compared to nerve stimulation infusion of glucagon led to a less pronounced increase of urate formation and a twice as large increase in glucose output but a decrease in lactate release without affecting the flow rate. Insulin had no effect on any of the parameters studied.

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Section: Discussionsupporting

confidence: 91%

Increase of urate formation by stimulation of sympathetic hepatic nerves, circulating noradrenaline and glucagon in the perfused rat liver

1987

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“…Such a result was surprising, since these agents have been shown to stimulate this pathway in many different cell types [25][26][27][28]. However, it is possible to activate the PPP without increasing PRPP levels [68,69]. It is also possible that an increase in PRPP in response to these agents was transient and not detected because of the time point chosen, or that, under the conditions of this experiment, metabolic pathways utilizing PRPP consumed this substrate before it could accumulate within the complexes.…”

Section: Discussionmentioning

confidence: 99%

Meiotic Induction in Cumulus Cell-Enclosed Mouse Oocytes: Involvement of the Pentose Phosphate Pathway1

Downs¹,

Humpherson²,

Leese³

1998

Biology of Reproduction

128

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In this study we tested the hypothesis that the pentose phosphate pathway (PPP) participates in the meiotic induction of mouse oocytes. The electron acceptors methylene blue, phenazine ethosulfate (PES), and pyrroline-5-carboxylate (P5C) oxidize NADPH to NADP and activate the NADP-dependent enzymes of the PPP. Each of these compounds triggered a dose-dependent increase in meiotic maturation in hypoxanthine-arrested cumulus cell-enclosed oocytes during 17- to 18-h cultures. More than 96% of the oocytes underwent germinal vesicle breakdown (GVB) at the highest concentrations of P5C and PES tested (250 and 1 microM, respectively) as compared to only 45-52% of control oocytes. P5C was also stimulatory to denuded oocytes. Analysis of energy substrates in microdrop cultures revealed a 3.6-fold increase in glucose consumption by PES-treated oocyte-cumulus cell complexes that was associated with stimulation of GVB. On the other hand, 2-deoxyglucose, which interferes with glucose utilization, prevented the induction of maturation brought about by P5C. Apocynin and diphenyleneiodonium, inhibitors of NADPH oxidase, prevented meiotic maturation in the presence or absence of FSH. Gonadotropin-induced maturation was also prevented by 6-aminonicotinamide (6-AN) and dehydroepiandrosterone (DHEA), inhibitors of the two NADP-dependent enzymes of the PPP, and this was accompanied by suppression of glucose consumption. Phosphoribosyl-pyrophosphate (PRPP) is an important compound required in purine metabolism and can be formed from the end product of the oxidative arm of the PPP, ribose-5-phosphate. Ribose, which can be metabolized to PRPP, increased PRPP synthesis in complexes and induced meiotic maturation when added to hypoxanthine-arrested cumulus cell-enclosed oocytes in glucose-free medium in both the presence and absence of FSH. PRPP levels within complexes were also increased by glucose and FSH, but were reduced by hypoxanthine, 6-AN, and DHEA. In addition, exogenous PRPP stimulated maturation in hypoxanthine-arrested oocytes. These results support the proposition that glucose metabolism through the PPP is important in the meiotic induction mechanism and may involve the generation of PRPP that acts, at least in part, through the purine metabolizing pathways.

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“…To examine the effect of the continuous supply of Hx on the increased rate of the de novo pathway by glucagon in liver (19), 0.5 mg of glucagon/200 g of body weight/12 h with or without Hx of 5.0 mol/200 g of body weight/12 h was similarly infused, and the metabolic rate of the de novo pathway in liver was determined. The stimulative effect of glucagon on the de novo purine synthesis in liver has been reported (19,20) and is applied to glucagon and insulin therapy for acute liver failure.…”

Section: Methodsmentioning

confidence: 99%

Amidophosphoribosyltransferase Limits the Rate of Cell Growth-linked de Novo Purine Biosynthesis in the Presence of Constant Capacity of Salvage Purine Biosynthesis

Yamaoka

Kondo

Honda

et al. 1997

Journal of Biological Chemistry

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Factors controlling relative flux rates of the de novo and salvage pathways of purine nucleotide biosynthesis during animal cell growth are not fully understood. To examine the relative role of each pathway for cell growth, three cell lines including CHO K1 (a wild-type Chinese hamster ovary fibroblast cell line), CHO ade ؊ A (an auxotrophic cell line deficient of amidophosphoribosyltransferase (ATase), a presumed rate-limiting enzyme of the de novo pathway), and CHO ade ؊ A transfected with human ATase cDNA ( ؊ A؉hATase) resulting in 30 -350% of the ATase activity of CHO K1, were cultured in purine-rich or purine-free media. Based on the enzyme activities of ATase and hypoxanthine phosphoribosyltransferase, the metabolic rate of the de novo and salvage pathways, the rate of cell growth (growth rate) in three cell lines under various culture conditions, and the effect of hypoxanthine infusion on the metabolic rate of the de novo pathway in rat liver, we concluded the following. 1) In ؊ A؉hATase transfectants, ATase activity limits the rate of the de novo pathway, which is closely linked with the growth rate. 2) Purine nucleotides are synthesized preferentially by the salvage pathway as long as hypoxanthine, the most essential source of purine salvage, can be utilized, which was confirmed in rat liver in vivo by hypoxanthine infusion. The preferential usage of the salvage pathway results in sparing the energy expenditure required for de novo synthesis.3) The regulatory capacity of the de novo pathway (about 200%) was larger than that of the salvage pathway (about 20%) with constant hypoxanthine phosphoribosyltransferase activity.Purine nucleotides synthesized via de novo and salvage pathways are indispensable for cell growth through DNA and RNA syntheses and for the ATP energy supply. Interference of purine metabolism has thus been the target of antineoplastic drugs. However, it is unclear which of the two pathways is more important for the supply of purine nucleotides during cell growth. Purine nucleotide synthesis catalyzed by HPRT, 1 the key enzyme of the purine salvage pathway, was reported to be more active than that catalyzed by ATase, the presumed ratelimiting enzyme of the de novo pathway, in many tissues and malignant cells (1, 2). The increased metabolic rate via the de novo pathway and ATase activity are, however, more strongly linked with cell growth and malignant transformation than the metabolic rate via the salvage pathway and HPRT activity (1, 3-7). To interpret this enigma, we investigated the mutual regulation of purine biosynthesis between the de novo and salvage pathways. The cDNA cloning of rat and human ATase (hATase) in our laboratory (8, 9), an ATase-deficient auxotrophic Chinese hamster ovary fibroblast cell line of CHO ade Ϫ A, and CHO ade Ϫ A transfected with hATase cDNA driven by the cytomegalovirus promoter ( Ϫ AϩhATase) enabled us to explore the rate-limiting property of ATase and to study the relationship between the two pathways in three cell lines in two purine-free or two purine-...

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Purine synthesis de novo and its regulation in rat hepatocytes

Cited by 14 publications

References 14 publications

Increase of urate formation by stimulation of sympathetic hepatic nerves, circulating noradrenaline and glucagon in the perfused rat liver

Increase of urate formation by stimulation of sympathetic hepatic nerves, circulating noradrenaline and glucagon in the perfused rat liver

Meiotic Induction in Cumulus Cell-Enclosed Mouse Oocytes: Involvement of the Pentose Phosphate Pathway1

Amidophosphoribosyltransferase Limits the Rate of Cell Growth-linked de Novo Purine Biosynthesis in the Presence of Constant Capacity of Salvage Purine Biosynthesis

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