The pentose phosphate pathwayThe pentose phosphate pathway (also called the phosphogluconate pathway and the hexose monophosphate shunt) is a parallel to. It generates and (5- ) as well as, the last one a precursor for the synthesis of nucleotides. While it does involve oxidation of, its primary role is rather than. The pathway is especially important in (erythrocytes).There are two distinct phases in the pathway. The first is the phase, in which NADPH is generated, and the second is the non-oxidative of 5-carbon sugars. For most organisms, the pentose phosphate pathway takes place in the; in plants, most steps take place in.Similar to, the pentose phosphate pathway appears to have a very ancient evolutionary origin.
![Lignin Lignin](/uploads/1/2/5/3/125373407/817064869.gif)
The reactions of this pathway are mostly enzyme-catalyzed in modern cells, however, they also occur non-enzymatically under conditions that replicate those of the ocean, and are catalyzed by, particularly ions (Fe(II)). This suggests that the origins of the pathway could date back to the prebiotic world. Contents.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. ). Production of (R5P), used in the synthesis of and nucleic acids.
Production of (E4P) used in the synthesis of.Aromatic amino acids, in turn, are precursors for many biosynthetic pathways, including the 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 power, accounting for approximately 60% of NADPH production in humans.
Protein phosphorylation is one of the most widespread forms of post-translational modification in eukaryotes. The addition of a phosphoryl group to serine, threonine, and tyrosine residues by a protein kinase can regulate activity, localization, stability, and protein–protein interaction networks of phosphorylation targets. Lignin (accounting for approximately 87% of linkages in softwood lignin 16) to detect the chemical stability of these seven linkages to reveal in details the sensitivity of lignin, the hydrolysis and phosphorylation occurring to the vulnerable linkages, and the process-tuned properties of the modified lignin. Results and Discussion 2.1.
One of the uses of NADPH in the cell is to prevent. It reduces via, which converts reactive H 2O 2 into H 2O. If absent, the H 2O 2 would be converted to hydroxyl free radicals by, 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.is also generated for in a process often referred to as a. Phases Oxidative phase In this phase, two molecules of + are reduced to, utilizing the energy from the conversion of into. 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:ReactantsProductsEnzymeDescription+ NADP+→ + NADPH. The hydroxyl on carbon 1 of glucose 6-phosphate turns into a carbonyl, generating a lactone, and, in the process, is generated.+ H 2O→ + H NADP +→ + NADPH + CO 2Oxidative. NADP + is the electron acceptor, generating another molecule of, a CO 2, and.The overall reaction for this process is:Glucose 6-phosphate + 2 NADP + + H 2O → ribulose 5-phosphate + 2 NADPH + 2 H + + CO 2 Non-oxidative phase.
The pentose phosphate pathway's nonoxidative phase ReactantsProductsEnzymes→→Ribulose 5-Phosphate 3-Epimerase+→ → → +Net reaction:3 ribulose-5-phosphate → 1 ribose-5-phosphate + 2 xylulose-5-phosphate → 2 fructose-6-phosphate + glyceraldehyde-3-phosphateRegulation is the rate-controlling enzyme of this pathway. It is stimulated by NADP + and strongly inhibited. 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 to produce more NADPH. This step is also inhibited. activity is also post-translationally regulated by cytoplasmic deacetylase. SIRT2-mediated deacetylation and activation of G6PD stimulates oxidative branch of PPP to supply cytosolic to counteract or support. Erythrocytes 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 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.
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See also. – A hereditary disease that disrupts the pentose phosphate pathway.References. Kruger, Nicholas J; von Schaewen, Antje (June 2003). 'The oxidative pentose phosphate pathway: structure and organisation'. Current Opinion in Plant Biology.
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