The pentose phosphate pathway is a metabolic pathway parallel to glycolysis. It generates NADPH and pentoses as well as ribose 5-phosphate, a precursor for the synthesis of nucleotides. While the pentose phosphate pathway does involve oxidation of glucose, its primary role is anabolic rather than catabolic. The pathway is especially important in red blood cells (erythrocytes).
Methylotrophs are a diverse group of microorganisms that can use reduced one-carbon compounds, such as methanol or methane, as the carbon source for their growth; and multi-carbon compounds that contain no carbon-carbon bonds, such as dimethyl ether and dimethylamine. This group of microorganisms also includes those capable of assimilating reduced one-carbon compounds by way of carbon dioxide using the ribulose bisphosphate pathway. These organisms should not be confused with methanogens which on the contrary produce methane as a by-product from various one-carbon compounds such as carbon dioxide. Some methylotrophs can degrade the greenhouse gas methane, and in this case they are called methanotrophs. The abundance, purity, and low price of methanol compared to commonly used sugars make methylotrophs competent organisms for production of amino acids, vitamins, recombinant proteins, single-cell proteins, co-enzymes and cytochromes.
6-Phosphogluconate dehydrogenase (6PGD) is an enzyme in the pentose phosphate pathway. It forms ribulose 5-phosphate from 6-phosphogluconate:
Ribose 5-phosphate (R5P) is both a product and an intermediate of the pentose phosphate pathway. The last step of the oxidative reactions in the pentose phosphate pathway is the production of ribulose 5-phosphate. Depending on the body's state, ribulose 5-phosphate can reversibly isomerize to ribose 5-phosphate. Ribulose 5-phosphate can alternatively undergo a series of isomerizations as well as transaldolations and transketolations that result in the production of other pentose phosphates as well as fructose 6-phosphate and glyceraldehyde 3-phosphate.
Phosphopentose epimerase encoded by the RPE gene is a metalloprotein that catalyzes the interconversion between D-ribulose 5-phosphate and D-xylulose 5-phosphate.
6-Phosphogluconolactonase (EC 3.1.1.31, 6PGL, PGLS, systematic name 6-phospho-D-glucono-1,5-lactone lactonohydrolase) is a cytosolic enzyme found in all organisms that catalyzes the hydrolysis of 6-phosphogluconolactone to 6-phosphogluconic acid in the oxidative phase of the pentose phosphate pathway:
Phosphoribosylformylglycinamidine cyclo-ligase is the fifth enzyme in the de novo synthesis of purine nucleotides. It catalyzes the reaction to form 5-aminoimidazole ribotide (AIR) from formylglycinamidine-ribonucleotide FGAM. This reaction closes the ring and produces a 5-membered imidazole ring of the purine nucleus (AIR):
In enzymology, an ascopyrone tautomerase is an enzyme that catalyzes the chemical reaction
In enzymology, a L-ribulose-5-phosphate 4-epimerase is an enzyme that catalyzes the interconversion of ribulose 5-phosphate and xylulose 5-phosphate in the oxidative phase of the Pentose phosphate pathway.
In enzymology, a phosphoribosylanthranilate isomerase (PRAI) is an enzyme that catalyzes the third step of the synthesis of the amino acid tryptophan.
Ribose-5-phosphate isomerase (Rpi) encoded by the RPIA gene is an enzyme that catalyzes the conversion between ribose-5-phosphate (R5P) and ribulose-5-phosphate (Ru5P). It is a member of a larger class of isomerases which catalyze the interconversion of chemical isomers. It plays a vital role in biochemical metabolism in both the pentose phosphate pathway and the Calvin cycle. The systematic name of this enzyme class is D-ribose-5-phosphate aldose-ketose-isomerase.
In enzymology, a S-methyl-5-thioribose-1-phosphate isomerase is an enzyme that catalyzes the chemical reaction
The enzyme 1,5-anhydro-D-fructose dehydratase (EC 4.2.1.111) catalyzes the chemical reaction
In enzymology, a formaldehyde transketolase is an enzyme that catalyzes the chemical reaction
Phosphoribulokinase (PRK) (EC 2.7.1.19) is an essential photosynthetic enzyme that catalyzes the ATP-dependent phosphorylation of ribulose 5-phosphate (RuP) into ribulose 1,5-bisphosphate (RuBP), both intermediates in the Calvin Cycle. Its main function is to regenerate RuBP, which is the initial substrate and CO2-acceptor molecule of the Calvin Cycle. PRK belongs to the family of transferase enzymes, specifically those transferring phosphorus-containing groups (phosphotransferases) to an alcohol group acceptor. Along with ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCo), phosphoribulokinase is unique to the Calvin Cycle. Therefore, PRK activity often determines the metabolic rate in organisms for which carbon fixation is key to survival. Much initial work on PRK was done with spinach leaf extracts in the 1950s; subsequent studies of PRK in other photosynthetic prokaryotic and eukaryotic organisms have followed. The possibility that PRK might exist was first recognized by Weissbach et al. in 1954; for example, the group noted that carbon dioxide fixation in crude spinach extracts was enhanced by the addition of ATP. The first purification of PRK was conducted by Hurwitz and colleagues in 1956.
ATP + Mg2+ - D-ribulose 5-phosphate ADP + D-ribulose 1,5-bisphosphate
3-Deoxy-D-arabinoheptulosonate 7-phosphate (DAHP) synthase is the first enzyme in a series of metabolic reactions known as the shikimate pathway, which is responsible for the biosynthesis of the amino acids phenylalanine, tyrosine, and tryptophan. Since it is the first enzyme in the shikimate pathway, it controls the amount of carbon entering the pathway. Enzyme inhibition is the primary method of regulating the amount of carbon entering the pathway. Forms of this enzyme differ between organisms, but can be considered DAHP synthase based upon the reaction that is catalyzed by this enzyme.
UDP-4-amino-4,6-dideoxy-N-acetyl-beta-L-altrosamine transaminase is an enzyme with systematic name UDP-4-amino-4,6-dideoxy-N-acetyl-beta-L-altrosamine:2-oxoglutarate aminotransferase. This enzyme catalyses the following chemical reaction
3-hexulose-6-phosphate synthase is an enzyme with systematic name D-arabino-hex-3-ulose-6-phosphate formaldehyde-lyase (D-ribulose-5-phosphate-forming). This enzyme catalyses the following chemical reaction
UDP-N-acetylglucosamine 4,6-dehydratase (configuration-inverting) (EC 4.2.1.115, FlaA1, UDP-N-acetylglucosamine 5-inverting 4,6-dehydratase, PseB, UDP-N-acetylglucosamine hydro-lyase (inverting, UDP-2-acetamido-2,6-dideoxy-β-L)arabino-hex-4-ulose-forming)) is an enzyme with systematic name UDP-N-acetyl-α-D-glucosamine hydro-lyase (inverting; UDP-2-acetamido-2,6-dideoxy-β-L-arabino-hex-4-ulose-forming). This enzyme catalyses the following chemical reaction
TDP-4-oxo-6-deoxy-alpha-D-glucose-3,4-oxoisomerase (dTDP-3-dehydro-6-deoxy-alpha-D-galactopyranose-forming) is an enzyme with systematic name dTDP-4-dehydro-6-deoxy-alpha-D-glucopyranose:dTDP-3-dehydro-6-deoxy-alpha-D-galactopyranose isomerase. This enzyme catalyses the following chemical reaction
