pentose shunt

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hexose monophosphate shunt、pentose phosphate pathway

WordNet

1. transfer to another track, of trains
2. a conductor having low resistance in parallel with another device to divert a fraction of the current (同)electrical shunt, bypass
3. implant consisting of a tube made of plastic or rubber; for draining fluids within the body
4. a passage by which a bodily fluid (especially blood) is diverted from one channel to another; "an arteriovenus shunt"
5. provide with or divert by means of an electrical shunt
6. avoid and stay away from deliberately; stay clear of (同)eschew
7. any monosaccharide sugar containing five atoms of carbon per molecule

PrepTutorEJDIC

1. 〈人・物〉‘を'わきにどかす;〈話題など〉‘を'他へそらす / (別の軌道に)〈車両〉‘を'入れ換える / 〈電流〉‘を'わきへそらす;〈分路〉‘を'置く / わきへそれる / 〈車両が〉分岐線に移行する / 〈U〉わきへそれること / 〈C〉転てつ器;(電気の)分路
2. …‘を'『避ける』(avoid)

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/11/19 14:03:12」(JST)

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The Pentose Phosphate Pathway

In biochemistry, the pentose phosphate pathway (also called the phosphogluconate pathway and the hexose monophosphate shunt) is a metabolic pathway parallel to glycolysis that generates NADPH and pentoses (5-carbon sugars). While it does involve oxidation of glucose, its primary role is anabolic rather than catabolic.

There are two distinct phases in the pathway. The first is the oxidative phase, in which NADPH is generated, and the second is the non-oxidative synthesis of 6-carbon sugars. For most organisms, the pentose phosphate pathway takes place in the cytosol; in plants, most steps take place in plastids.

Similar to glycolysis, the pentose phosphate pathway appears to have a very ancient evolutionary origin. The reactions of this pathway are mostly enzyme-catalyzed in modern cells. They also occur however non-enzymatically under conditions that replicate those of the Archean ocean, and are catalyzed by metal ions, ferrous ions (Fe(II)) in particular. The origins of the pathway could thus date back to the prebiotic world.

Outcome

The primary results of the pathway are:

• The generation of reducing equivalents, in the form of NADPH, used in reductive biosynthesis reactions within cells (e.g. fatty acid synthesis).
• Production of ribose 5-phosphate (R5P), used in the synthesis of nucleotides and nucleic acids.
• Production of erythrose 4-phosphate (E4P) used in the synthesis of aromatic amino acids.

Aromatic amino acids, in turn, are precursors for many biosynthetic pathways, including the lignin in wood.

Dietary pentose sugars derived from the digestion of nucleic acids may be metabolized through the pentose phosphate pathway, and the carbon skeletons of dietary carbohydrates may be converted into glycolytic/gluconeogenic intermediates.

In mammals, the PPP occurs exclusively in the cytoplasm, and is found to be most active in the liver, mammary gland and adrenal cortex in the human. The PPP is one of the three main ways the body creates molecules with reducing power, accounting for approximately 60% of NADPH production in humans.

One of the uses of NADPH in the cell is to prevent oxidative stress. It reduces glutathione via glutathione reductase, which converts reactive H₂O₂ into H₂O by glutathione peroxidase. If absent, the H₂O₂ would be converted to hydroxyl free radicals by Fenton chemistry, which can attack the cell. Erythrocytes, for example, generate a large amount of NADPH through the pentose phosphate pathway to use in the reduction of glutathione.

Hydrogen peroxide is also generated for phagocytes in a process often referred to as a respiratory burst.

Phases

Oxidative phase

In this phase, two molecules of NADP⁺ are reduced to NADPH, utilizing the energy from the conversion of glucose-6-phosphate into ribulose 5-phosphate.

Oxidative phase of pentose phosphate pathway.

Glucose-6-phosphate (1), 6-phosphoglucono-δ-lactone (2), 6-phosphogluconate (3), ribulose 5-phosphate (4)

The entire set of reactions can be summarized as follows:

Reactants	Products	Enzyme	Description
Glucose 6-phosphate + NADP+	→ 6-phosphoglucono-δ-lactone + NADPH	glucose 6-phosphate dehydrogenase	Dehydrogenation. The hydroxyl on carbon 1 of glucose 6-phosphate turns into a carbonyl, generating a lactone, and, in the process, NADPH is generated.
6-phosphoglucono-δ-lactone + H2O	→ 6-phosphogluconate + H+	6-phosphogluconolactonase	Hydrolysis
6-phosphogluconate + NADP+	→ ribulose 5-phosphate + NADPH + CO2	6-phosphogluconate dehydrogenase	Oxidative decarboxylation. NADP+ is the electron acceptor, generating another molecule of NADPH, a CO2, and ribulose 5-phosphate.

The overall reaction for this process is:

Glucose 6-phosphate + 2 NADP⁺ + H₂O → ribulose 5-phosphate + 2 NADPH + 2 H⁺ + CO₂

Non-oxidative phase

The pentose phosphate pathway's nonoxidative phase

Reactants	Products	Enzymes
ribulose 5-phosphate	→ ribose 5-phosphate	Ribulose 5-Phosphate Isomerase
ribulose 5-phosphate	→ xylulose 5-phosphate	Ribulose 5-Phosphate 3-Epimerase
xylulose 5-phosphate + ribose 5-phosphate	→ glyceraldehyde 3-phosphate + sedoheptulose 7-phosphate	transketolase
sedoheptulose 7-phosphate + glyceraldehyde 3-phosphate	→ erythrose 4-phosphate + fructose 6-phosphate	transaldolase
xylulose 5-phosphate + erythrose 4-phosphate	→ glyceraldehyde 3-phosphate + fructose 6-phosphate	transketolase

Net reaction: 3 ribulose-5-phosphate → 1 ribose-5-phosphate + 2 xylulose-5-phosphate → 2 fructose-6-phosphate + glyceraldehyde-3-phosphate

Regulation

Glucose-6-phosphate dehydrogenase is the rate-controlling enzyme of this pathway. It is allosterically stimulated by NADP⁺ and strongly inhibited by NADPH. The ratio of NADPH:NADP⁺ is normally about 100:1 in liver cytosol. This makes the cytosol a highly-reducing environment. An NADPH-utilizing pathway forms NADP⁺, which stimulates Glucose-6-phosphate dehydrogenase to produce more NADPH. This step is also inhibited by acetyl CoA.

G6PD activity is also post-translationally regulated by cytoplasmic deacetylase SIRT2. SIRT2-mediated deacetylation and activation of G6PD stimulates pentose phosphate pathway to supply cytosolic NADPH to counteract oxidative damage.

Erythrocytes and the pentose phosphate pathway

Several deficiencies in the level of activity (not function) of glucose-6-phosphate dehydrogenase have been observed to be associated with resistance to the malarial parasite Plasmodium falciparum among individuals of Mediterranean and African descent. The basis for this resistance may be a weakening of the red cell membrane (the erythrocyte is the host cell for the parasite) such that it cannot sustain the parasitic life cycle long enough for productive growth.

See also

• G6PDH deficiency - A hereditary disease that disrupts the pentose phosphate pathway
• RNA
• Thiamine deficiency
• Frank Dickens FRS

References

External links

• The chemical logic behind the pentose phosphate pathway
• Pentose Phosphate Pathway at the US National Library of Medicine Medical Subject Headings (MeSH)
• Pentose phosphate pathway Map - Homo sapiens

UpToDate Contents

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• 1. 中枢神経系シャントおよび他のデバイスの感染 infections of central nervous system shunts and other devices
• 2. グルコース-6-リン酸脱水素酵素欠損症の遺伝学および病態生理 genetics and pathophysiology of glucose 6 phosphate dehydrogenase deficiency
• 3. メトヘモグロビン血症の遺伝学および病因 genetics and pathogenesis of methemoglobinemia
• 4. 左右シャントの病態生理 pathophysiology of left to right shunts
• 5. Eisenmenger症候群の評価および予後 evaluation and prognosis of eisenmenger syndrome

English Journal

• Energy status regulates disease development and respiratory metabolism of Lasiodiplodia theobromae (Pat.) Griff. & Maubl.-infected longan fruit.

• Zhang S1, Lin H2, Lin Y1, Lin Y1, Hung YC3, Chen Y1, Wang H1, Shi J4.
• Food chemistry.Food Chem.2017 Sep 15;231:238-246. doi: 10.1016/j.foodchem.2017.03.132. Epub 2017 Mar 23.
• PMID 28450002

• Altered glycometabolism in zebrafish exposed to thifluzamide.

• Yang Y1, Liu W2, Li D1, Qian L1, Fu B3, Wang C4.
• Chemosphere.Chemosphere.2017 Sep;183:89-96. doi: 10.1016/j.chemosphere.2017.05.055. Epub 2017 May 10.
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• Exploring the neuroprotective effects of ginkgolides injection in a rodent model of cerebral ischemia-reperfusion injury by GC-MS based metabolomic profiling.

• Geng JL1, Aa JY1, Feng SQ1, Wang SY2, Wang P1, Zhang Y1, Ouyang BC1, Wang JK1, Zhu YJ1, Huang WZ2, Wang ZZ2, Xiao W3, Wang GJ4.
• Journal of pharmaceutical and biomedical analysis.J Pharm Biomed Anal.2017 Aug 5;142:190-200. doi: 10.1016/j.jpba.2017.04.031. Epub 2017 Apr 23.
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Japanese Journal

• 酵母Gcy1pはエリスロースとエリスロース-4-リン酸を還元する

• 大倉 哲也,春見 隆文
• 食品総合研究所研究報告 (71), 57-60, 2007-03
• NAID 40015416848

• Modulation of talA Gene in Pentose Phosphate Pathway for Overproduction of Poly-β-Hydroxybutyrate in Transformant Escherichia coli Harboring phbCAB Operon(GENETICS, MOLECULAR BIOLOGY, AND GENE ENGINEERING)

• Song Byoung-Geun,Kim Tae-Kwon,Jung Young-Mi,Lee Yong-Hyun
• Journal of bioscience and bioengineering 102(3), 237-240, 2006-09-25
• … The talA gene encoding transaldolase, the key enzyme in the nonoxidative pentose phosphate pathway, was amplified in a transformant Escherichia coli harboring the phbCAB operon to shift the metabolic flux of the hexose mono-phosphate shunt to the odd-ball biosynthesis pathway for poly-β-hydroxybutyrate overproduction. …
• NAID 110004809599

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