pentose-phosphate shunt
Definition
Target type: biologicalprocess
The metabolic process in which glucose-6-phosphate is oxidized to form carbon dioxide (CO2) and ribulose 5-phosphate, coupled to reduction of NADP+ to NADPH; ribulose 5-P then enters a series of reactions that can yield biosynthetic precursors (ribose-5-phosphate and erythrose-4-phosphate) and glycolytic intermediates (fructose-6-phosphate and glyceraldehyde-3-phosphate). [GOC:pde, ISBN:0198506732, MetaCyc:PENTOSE-P-PWY]
The pentose phosphate pathway (PPP), also known as the hexose monophosphate shunt, is an alternative glucose catabolic pathway that operates alongside glycolysis. Unlike glycolysis, which primarily focuses on ATP production, the PPP primarily produces NADPH, a reducing agent essential for anabolic reactions, and pentose sugars, primarily ribose-5-phosphate, crucial for nucleotide biosynthesis.
The PPP consists of two distinct phases: the oxidative phase and the non-oxidative phase.
**Oxidative Phase:**
1. Glucose-6-phosphate dehydrogenase (G6PD) catalyzes the first committed step, oxidizing glucose-6-phosphate to 6-phosphogluconolactone using NADP+ as an electron acceptor, generating NADPH.
2. 6-Phosphogluconolactonase hydrolyzes the lactone ring, yielding 6-phosphogluconate.
3. 6-Phosphogluconate dehydrogenase further oxidizes 6-phosphogluconate to ribulose-5-phosphate, again using NADP+ as an electron acceptor and producing NADPH.
This phase generates two molecules of NADPH and one molecule of ribulose-5-phosphate per glucose-6-phosphate molecule.
**Non-Oxidative Phase:**
1. Ribulose-5-phosphate isomerase converts ribulose-5-phosphate to ribose-5-phosphate, a precursor for nucleotide biosynthesis.
2. Ribose-5-phosphate epimerase converts ribose-5-phosphate to xylulose-5-phosphate.
3. Transketolase and transaldolase catalyze a series of complex rearrangements, interconverting sugars with 3, 4, 5, 6, and 7 carbons. These reactions allow the pathway to produce the necessary amounts of ribose-5-phosphate, as well as glycolytic intermediates like fructose-6-phosphate and glyceraldehyde-3-phosphate, enabling the pathway to be integrated with glycolysis.
**Functions of the Pentose Phosphate Shunt:**
1. **NADPH Production:** NADPH is essential for reducing power in various anabolic reactions, including fatty acid biosynthesis, steroid hormone biosynthesis, and detoxification reactions, particularly in red blood cells to protect against oxidative damage.
2. **Ribose-5-phosphate Production:** Ribose-5-phosphate is a precursor for nucleotide biosynthesis, crucial for DNA, RNA, and coenzyme synthesis.
3. **Intermediates for Glycolysis:** The non-oxidative phase can generate glycolytic intermediates, allowing the PPP to contribute to glucose metabolism and ATP production.
4. **Red Blood Cell Function:** The PPP is particularly active in red blood cells, where NADPH is essential for reducing oxidative stress caused by reactive oxygen species.
The PPP plays a vital role in maintaining cellular redox balance, providing building blocks for biosynthesis, and contributing to overall energy metabolism.'"
Proteins (4)
| Protein | Definition | Taxonomy |
|---|---|---|
| 6-phosphogluconate dehydrogenase, decarboxylating | A 6-phosphogluconate dehydrogenase, decarboxylating that is encoded in the genome of human. [PRO:DNx, UniProtKB:P52209] | Homo sapiens (human) |
| Transketolase | A transketolase that is encoded in the genome of human. [PRO:DNx, UniProtKB:P29401] | Homo sapiens (human) |
| Glucose-6-phosphate 1-dehydrogenase | A glucose-6-phosphate 1-dehydrogenase that is encoded in the genome of human. [PRO:DNx, UniProtKB:P11413] | Homo sapiens (human) |
| Acetyl-CoA carboxylase 2 | An acetyl-CoA carboxylase 2 that is encoded in the genome of human. [PRO:DNx, UniProtKB:O00763] | Homo sapiens (human) |
Compounds (37)
| Compound | Definition | Classes | Roles |
|---|---|---|---|
| thiamine | thiamine(1+) : A primary alcohol that is 1,3-thiazol-3-ium substituted by (4-amino-2-methylpyrimidin-5-yl)methyl, methyl and 2-hydroxyethyl groups at positions 3, 4 and 5, respectively. | primary alcohol; vitamin B1 | Escherichia coli metabolite; human metabolite; mouse metabolite; Saccharomyces cerevisiae metabolite |
| furosemide | furosemide : A chlorobenzoic acid that is 4-chlorobenzoic acid substituted by a (furan-2-ylmethyl)amino and a sulfamoyl group at position 2 and 5 respectively. It is a diuretic used in the treatment of congestive heart failure. Furosemide: A benzoic-sulfonamide-furan. It is a diuretic with fast onset and short duration that is used for EDEMA and chronic RENAL INSUFFICIENCY. | chlorobenzoic acid; furans; sulfonamide | environmental contaminant; loop diuretic; xenobiotic |
| ketotifen | ketotifen : An organic heterotricyclic compound that is 4,9-dihydro-10H-benzo[4,5]cyclohepta[1,2-b]thiophen-10-one which is substituted at position 4 by a 1-methylpiperidin-4-ylidene group. A blocker of histamine H1 receptors with a stabilising action on mast cells, it is used (usually as its hydrogen fumarate salt) for the treatment of asthma, where it may take several weeks to exert its full effect. Ketotifen: A cycloheptathiophene blocker of histamine H1 receptors and release of inflammatory mediators. It has been proposed for the treatment of asthma, rhinitis, skin allergies, and anaphylaxis. | cyclic ketone; olefinic compound; organic heterotricyclic compound; organosulfur heterocyclic compound; piperidines; tertiary amino compound | anti-asthmatic drug; H1-receptor antagonist |
| metoclopramide | metoclopramide : A member of the class of benzamides resulting from the formal condensation of 4-amino-5-chloro-2-methoxybenzoic acid with the primary amino group of N,N-diethylethane-1,2-diamine. Metoclopramide: A dopamine D2 antagonist that is used as an antiemetic. | benzamides; monochlorobenzenes; substituted aniline; tertiary amino compound | antiemetic; dopaminergic antagonist; environmental contaminant; gastrointestinal drug; xenobiotic |
| thymidine | pyrimidine 2'-deoxyribonucleoside | Escherichia coli metabolite; human metabolite; metabolite; mouse metabolite | |
| methylprednisolone acetate | methylprednisolone acetate : An acetate ester resulting from the formal condensation of the 21-hydroxy function of 6alpha-methylprednisolone compound with acetic acid. Methylprednisolone Acetate: Methylprednisolone derivative that is used as an anti-inflammatory agent for the treatment of ALLERGY and ALLERGIC RHINITIS; ASTHMA; and BURSITIS; and for the treatment of ADRENAL INSUFFICIENCY. | 11beta-hydroxy steroid; 17alpha-hydroxy steroid; 20-oxo steroid; 3-oxo-Delta(1),Delta(4)-steroid; acetate ester; glucocorticoid; steroid ester; tertiary alpha-hydroxy ketone | anti-inflammatory drug |
| androsterone | 17-oxo steroid; 3alpha-hydroxy steroid; androstanoid; C19-steroid | androgen; anticonvulsant; human blood serum metabolite; human metabolite; human urinary metabolite; mouse metabolite; pheromone | |
| dehydroepiandrosterone | dehydroepiandrosterone : An androstanoid that is androst-5-ene substituted by a beta-hydroxy group at position 3 and an oxo group at position 17. It is a naturally occurring steroid hormone produced by the adrenal glands. Dehydroepiandrosterone: A major C19 steroid produced by the ADRENAL CORTEX. It is also produced in small quantities in the TESTIS and the OVARY. Dehydroepiandrosterone (DHEA) can be converted to TESTOSTERONE; ANDROSTENEDIONE; ESTRADIOL; and ESTRONE. Most of DHEA is sulfated (DEHYDROEPIANDROSTERONE SULFATE) before secretion. | 17-oxo steroid; 3beta-hydroxy-Delta(5)-steroid; androstanoid | androgen; human metabolite; mouse metabolite |
| pregnenolone | 20-oxo steroid; 3beta-hydroxy-Delta(5)-steroid; C21-steroid | human metabolite; mouse metabolite | |
| epigallocatechin gallate | (-)-epigallocatechin 3-gallate : A gallate ester obtained by the formal condensation of gallic acid with the (3R)-hydroxy group of (-)-epigallocatechin. epigallocatechin gallate: a steroid 5alpha-reductase inhibitor and antimutagen in green tea (Camellia sinensis) | flavans; gallate ester; polyphenol | antineoplastic agent; antioxidant; apoptosis inducer; geroprotector; Hsp90 inhibitor; neuroprotective agent; plant metabolite |
| 16-bromoepiandrosterone | 16alpha-bromo-3beta-hydroxy-5alpha-androstan-17-one: a synthetic adrenal hormone that reduced the incidence of tuberculosis and other opportunistic infections in AIDS patients | ||
| epicatechin | (-)-epicatechin : A catechin with (2R,3R)-configuration. | catechin; polyphenol | antioxidant |
| gallocatechol | (-)-epigallocatechin : A flavan-3,3',4',5,5',7-hexol having (2R,3R)-configuration. | catechin; flavan-3,3',4',5,5',7-hexol | antioxidant; food component; plant metabolite |
| (-)-catechin | (-)-catechin : The (-)-enantiomer of catechin. | catechin | metabolite |
| brexanolone | brexanolone : A 3-hydroxy-5alpha-pregnan-20-one in which the hydroxy group at position 3 has alpha-configuration. It is a metabolite of the sex hormone progesterone and used for the treatment of postpartum depression in women. brexanolone: a mixture of allopregnanolone and sulfobutylether‐beta‐cyclodextrin for treatment of postpartum depression | 3-hydroxy-5alpha-pregnan-20-one | antidepressant; GABA modulator; human metabolite; intravenous anaesthetic; sedative |
| tetrahydrodeoxycorticosterone | tetrahydrodeoxycorticosterone: RN given refers to (3alpha,5beta)-isomer | 21-hydroxy steroid | |
| 16-hydroxydehydroepiandrosterone | 16-hydroxydehydroepiandrosterone: RN refers to (3beta,16alpha)-isomer | 16alpha-hydroxy steroid; 17-oxo steroid; 3beta-hydroxy-Delta(5)-steroid; androstanoid; secondary alpha-hydroxy ketone | human metabolite; mouse metabolite |
| epicatechin gallate | (-)-epicatechin-3-O-gallate : A gallate ester obtained by formal condensation of the carboxy group of gallic acid with the (3R)-hydroxy group of epicatechin. A natural product found in Parapiptadenia rigida. epicatechin gallate: a steroid 5alpha-reductase inhibitor; RN given refers to the (cis)-isomer; structure given in first source; isolated from green tea | catechin; gallate ester; polyphenol | EC 3.2.1.1 (alpha-amylase) inhibitor; EC 3.2.1.20 (alpha-glucosidase) inhibitor; metabolite |
| thiamine thiazolone pyrophosphate | thiamine thiazolone pyrophosphate: structure | ||
| methotrexate | dicarboxylic acid; monocarboxylic acid amide; pteridines | abortifacient; antimetabolite; antineoplastic agent; antirheumatic drug; dermatologic drug; DNA synthesis inhibitor; EC 1.5.1.3 (dihydrofolate reductase) inhibitor; immunosuppressive agent | |
| (-)-gallocatechin gallate | (-)-gallocatechin gallate : A gallate ester obtained by formal condensation of the carboxy group of gallic acid with the (3R)-hydroxy group of (-)-gallocatechin. A natural product found in found in green tea. | catechin; gallate ester; polyphenol | antineoplastic agent; EC 3.4.22.69 (SARS coronavirus main proteinase) inhibitor; human xenobiotic metabolite; plant metabolite |
| 21-hydroxypregnenolone | 21-hydroxypregnenolone : A hydroxypregnenolone that is pregnenolone which has been substituted by a hydroxy group at position 21. 21-hydroxypregnenolone: RN given refers to (3beta)-isomer; | 21-hydroxy steroid; hydroxypregnenolone; primary alpha-hydroxy ketone | mouse metabolite |
| epiandrosterone | epiandrosterone : A 3beta-hydroxy steroid that is (5alpha)-androstane substituted by a beta-hydroxy group at position 3 and an oxo group at position 17. | 17-oxo steroid; 3beta-hydroxy steroid; androstanoid | androgen; human metabolite |
| cp-640186 | CP-640186: a potent inhibitor of mammalian Acetyl-coenzyme A carboxylases & can reduce body weight and improve insulin sensitivity in test animals; structure in first source | anthracenes; bipiperidines; morpholines; N-acylpiperidine | |
| 4-phospho-d-erythronohydroxamic acid | |||
| 4-phosphoerythronate | 4-phospho-D-erythronic acid : The D-enantiomer of 4-phosphoerythronic acid. 4-phosphoerythronate: inhibits ribose-5-phosphate isomerase | 4-phosphoerythronic acid | Escherichia coli metabolite; mouse metabolite |
| paricalcitol | hydroxy seco-steroid; seco-cholestane | antiparathyroid drug | |
| polydatin | trans-piceid : A stilbenoid that is trans-resveratrol substituted at position 3 by a beta-D-glucosyl residue. | beta-D-glucoside; monosaccharide derivative; polyphenol; stilbenoid | anti-arrhythmia drug; antioxidant; geroprotector; hepatoprotective agent; metabolite; nephroprotective agent; potassium channel modulator |
| wedelolactone | wedelolactone : A member of the class of coumestans that is coumestan with hydroxy substituents as positions 1, 8 and 9 and a methoxy substituent at position 3. wedelolactone: antihepatotoxic coumestan from Eclipta prostrata and Wedelia calendulacea (both Asteraceae); structure given in first source | aromatic ether; coumestans; delta-lactone; polyphenol | antineoplastic agent; apoptosis inducer; EC 5.99.1.3 [DNA topoisomerase (ATP-hydrolysing)] inhibitor; hepatoprotective agent; metabolite |
| quercetin | |||
| (-)-catechin-3-O-gallate | (-)-catechin-3-O-gallate : A gallate ester obtained by formal condensation of the carboxy group of gallic acid with the (3R)-hydroxy group of (-)-catechin. | flavans; gallate ester; polyphenol | metabolite |
| indigo carmine | 3,5-di-O-(E)-caffeoylquinic acid: from roots of Lychnophora ericoides; structure in first source 3,5-di-O-caffeoyl quinic acid : A carboxylic ester that is the diester obtained by the condensation of the hydroxy groups at positions 3 and 5 of (-)-quinic acid with the carboxy group of trans-caffeic acid. Isolated from Brazilian propolis and Suaeda glauca, it exhibits hepatoprotective and cytotoxic activities. | ||
| thiocolchicoside | thiocolchicoside: used in combination with glafenine and meprobamate to tranquilize patients undergoing hysterosalpingography; structure | glycoside | |
| 3,5-dichloro-2-hydroxy-N-(2-methoxy-5-phenylphenyl)benzenesulfonamide | biphenyls | ||
| ml276 | |||
| mobic | meloxicam : A benzothiazine that is piroxicam in which the pyridin-2-yl group is replaced by a 5-methyl-1,3-thiazol-2-yl group. A non-steroidal anti-inflammatory drug and selective inhibitor of COX-2, it is used particularly for the management of rheumatoid arthritis. Meloxicam: A benzothiazine and thiazole derivative that acts as a NSAID and cyclooxygenase-2 (COX-2) inhibitor. It is used in the treatment of RHEUMATOID ARTHRITIS; OSTEOARTHRITIS; and ANKYLOSING SPONDYLITIS. | 1,3-thiazoles; benzothiazine; monocarboxylic acid amide | analgesic; antirheumatic drug; cyclooxygenase 2 inhibitor; non-steroidal anti-inflammatory drug |
| olanzapine | olanzapine : A benzodiazepine that is 10H-thieno[2,3-b][1,5]benzodiazepine substituted by a methyl group at position 2 and a 4-methylpiperazin-1-yl group at position 4. Olanzapine: A benzodiazepine derivative that binds SEROTONIN RECEPTORS; MUSCARINIC RECEPTORS; HISTAMINE H1 RECEPTORS; ADRENERGIC ALPHA-1 RECEPTORS; and DOPAMINE RECEPTORS. It is an antipsychotic agent used in the treatment of SCHIZOPHRENIA; BIPOLAR DISORDER; and MAJOR DEPRESSIVE DISORDER; it may also reduce nausea and vomiting in patients undergoing chemotherapy. | benzodiazepine; N-arylpiperazine; N-methylpiperazine | antiemetic; dopaminergic antagonist; histamine antagonist; muscarinic antagonist; second generation antipsychotic; serotonergic antagonist; serotonin uptake inhibitor |