The pentose phosphate pathway's Nonoxidative phase

The pentose phosphate pathway (also called Phosphogluconate Pathway, or Hexose Monophosphate Shunt [HMP shunt]) is a process that serves to generate NADPH and the synthesis of pentose (5-carbon) sugars. 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 5 carbon sugars. The pathway is one of the three main ways the body creates reducing molecules to prevent oxidative stress, accounting for approximately 10% of NADPH production in humans. It reduces the coenzyme glutathione which converts reactive H₂O₂ into H₂O. If absent, the H₂O₂ would be converted to hydroxyl free radicals which can attack the cell. Image File history File links Ppp. ... Image File history File links Ppp. ... Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... Magnification of typical sugar showing monoclinic hemihedral crystalline structure. ... The most fundamental reactions in chemistry are the redox processes. ... The most fundamental reactions in chemistry are the redox processes. ... Oxidative stress is a medical term for damage to animal or plant cells (and thereby the organs and tissues composed of those cells) caused by reactive oxygen species, which include (but are not limited to) superoxide, singlet oxygen, peroxynitrite or hydrogen peroxide. ...

Oxidative phase

In this phase, two molecules of NADP⁺ are reduced to NADPH, utilising the energy from the conversion of glucose-6-phosphate into ribulose 5-phosphate. Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. ... Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. ... Glucose 6-phosphate is glucose sugar phosphorylated on carbon 6. ... Fischer projection of D-ribulose Ribulose is a ketopentose — a monosaccharide containing five carbon atoms, and including a ketone functional group. ...

The overall reaction for this process is:
Glucose 6-phosphate + 2 NADP⁺ + H₂O → ribulose 5-phosphate + 2 NADPH + 2 H⁺ + CO₂

The first step in this series of reactions is the dehydrogenation of glucose 6-phosphate into 6-phosphoglucono-δ-lactone. This reaction is catalyzed by glucose 6-phosphate dehydrogenase. The hydroxyl group located on carbon 1 of glucose 6-phosphate is converted into a keto group, and in the process, NADPH is generated. Hydrogenation is a chemical reaction in which unsaturated bonds between carbon atoms are reduced by attachment of a hydrogen atom to each carbon. ... Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. ...

The second step is the hydrolysis of 6-phosphoglucono-δ-lactone to 6-phosphogluconate, which is catalyzed by 6-phosphoglucolactonase. Hydrolysis is a chemical reaction or process in which a molecule is split into two parts by reacting with a molecule of water, which has the chemical formula H2O. One of the parts gets an OH- from the water molecule and the other part gets an H+ from the water. ...

The third step is the oxidative decarboxylation of 6-phosphogluconate to ribulose 5-phosphate. This reaction is catalyzed by 6-phosphogluconate dehydrogenase and NADP⁺ is the electron acceptor, generating another molecule of NADPH. A Decarboxylation is any chemical reaction in which a carboxyl group (-COOH) is split off from a compound as carbon dioxide (CO2). ... Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. ...

The final step is the isomerization (catalyzed by phosphopentose isomerase) of ribulose 5-phosphate into ribose 5-phosphate. In chemistry, isomerization is the transformation of a molecule into a different isomer. ...

The entire set of reactions can be summarized as follows:

1. Glucose 6-phosphate + NADP+ → 6-phosphoglucono-δ-lactone + NADPH
2. 6-phosphoglucono-δ-lactone + H₂O → 6-phosphogluconate + H⁺
3. 6-phosphogluconate + NADP⁺ → ribulose 5-phosphate + NADPH + CO₂

Oxidative phase of pentose phosphate pathway

Image File history File links Download high resolution version (983x106, 5 KB) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...

Non-oxidative phase

1. ribulose 5-phosphate → ribose 5-phosphate (phosphopentose isomerase)
2. ribulose 5-phosphate → xylulose 5-phosphate (phosphopentose epimerase)
3. xylulose 5-phosphate + ribose 5-phosphate → glyceraldehyde 3-phosphate + sedoheptulose 7-phosphate (transketolase)
4. sedoheptulose 7-phosphate + glyceraldehyde 3-phosphate → erythrose 4-phosphate + fructose 6-phosphate (transaldolase)
5. xylulose 5-phosphate + erythrose 4-phosphate → glyceraldehyde 3-phosphate + fructose 6-phosphate (transketolase)

For a thorough scientific overview of ribose-5-phosphate isomerase deficiency and transaldolase deficiency, one can consult the supplement of chapter 73 in OMMBID^[1]. For more online resources and references, see inborn error of metabolism.
Sedoheptulose is a keto-heptose - a simple sugar with 5 carbon atoms and a ketone functional group. ... Transketolase and the Reactions of Thiamin Pyrophosphate Transketolase, an enzyme of the Calvin Cycle of photosynthesis, catalyzes the transfer of a 2-carbon fragment from a 5-carbon keto sugar (D-xyulose-5-P) to a 5-carbon aldo sugar (D-ribose-5-P) to form a 7-carbon keto... Inborn errors of metabolism comprise a large class of genetic diseases involving disorders of metabolism. ...

See also

• G6PDH deficiency - A hereditary disease which disrupts the pentose phosphate pathway.
• NADPH
• RNA

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked recessive hereditary disease featuring nonimmune hemolytic anemia in response to a number of causes. ... Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. ... Ribonucleic acid (RNA) is a nucleic acid polymer consisting of nucleotide monomers. ...

External links

• The chemical logic behind the pentose phosphate pathway

References

1. ^ Charles Scriver, Beaudet, A.L., Valle, D., Sly, W.S., Vogelstein, B., Childs, B., Kinzler, K.W. (2006). The Online Metabolic and Molecular Bases of Inherited Disease. New York: McGraw-Hill. - Free summaries of 255 chapters, full text through many universities and organizations. There is also the OMMBID blog.