Thiamine pyrophosphate

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Thiamine pyrophosphate
Thiamine diphosphate.png
Names
IUPAC name
2-[3-[(4-amino-2-methylpyrimidin-5-yl)methyl]-4-methyl-1,3-thiazol-3-ium-5-yl]ethyl phosphono hydrogen phosphate
Other names
Thiamine diphosphate
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
KEGG
MeSH Thiamine+pyrophosphate
PubChem CID
UNII
  • InChI=1S/C12H17N4OS.ClH.H4O7P2/c1-8-11(3-4-17)18-7-16(8)6-10-5-14-9(2)15-12(10)13;;1-8(2,3)7-9(4,5)6/h5,7,17H,3-4,6H2,1-2H3,(H2,13,14,15);1H;(H2,1,2,3)(H2,4,5,6)/q+1;;/p-1 Yes check.svgY
    Key: NBSUTVXQOGUTJX-UHFFFAOYSA-M Yes check.svgY
  • InChI=1/C12H17N4OS.ClH.H4O7P2/c1-8-11(3-4-17)18-7-16(8)6-10-5-14-9(2)15-12(10)13;;1-8(2,3)7-9(4,5)6/h5,7,17H,3-4,6H2,1-2H3,(H2,13,14,15);1H;(H2,1,2,3)(H2,4,5,6)/q+1;;/p-1
    Key: NBSUTVXQOGUTJX-REWHXWOFAB
  • Cc2ncc(C[n+]1csc(CCOP(=O)(O)OP(=O)(O)O)c1C)c(N)n2
Properties
C12H19N4O7P2S+
Molar mass 425.314382 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Thiamine pyrophosphate (TPP or ThPP), or thiamine diphosphate (ThDP), or cocarboxylase [1] is a thiamine (vitamin B1) derivative which is produced by the enzyme thiamine diphosphokinase. Thiamine pyrophosphate is a cofactor that is present in all living systems, in which it catalyzes several biochemical reactions.

Contents

Thiamine pyrophosphate is synthesized in the cytosol and is required in the cytosol for the activity of transketolase and in the mitochondria for the activity of pyruvate-, oxoglutarate- and branched chain keto acid dehydrogenases. To date, the yeast ThPP carrier (Tpc1p) the human Tpc and the Drosophila melanogaster have been identified as being responsible for the mitochondrial transport of ThPP and ThMP. [2] [3] [4] It was first discovered as an essential nutrient (vitamin) in humans through its link with the peripheral nervous system disease beriberi, which results from a deficiency of thiamine in the diet. [5]

TPP works as a coenzyme in many enzymatic reactions, such as:

Chemistry

The "ylide form" of TPP. TPP-ylide.svg
The "ylide form" of TPP.

Chemically, TPP consists of a pyrimidine ring which is connected to a thiazole ring, which is in turn connected to a pyrophosphate (diphosphate) functional group.

The part of TPP molecule that is most commonly involved in reactions is the thiazole ring, which contains nitrogen and sulfur. Thus, the thiazole ring is the "reagent portion" of the molecule. The C2 of this ring is capable of acting as an acid by donating its proton and forming a carbanion. [7] Normally, reactions that form carbanions are highly unfavorable, but the positive charge on the tetravalent nitrogen just adjacent to the carbanion stabilizes the negative charge, making the reaction much more favorable. [7] A compound with positive and negative charges on adjacent atoms is called an ylide, so sometimes the carbanion form of TPP is referred to as the "ylide form". [5] [8]

Reaction mechanisms

In several reactions, including that of pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase, TPP catalyses the reversible decarboxylation reaction (aka cleavage of a substrate compound at a carbon-carbon bond connecting a carbonyl group to an adjacent reactive group—usually a carboxylic acid or an alcohol). It achieves this in four basic steps:

  1. The carbanion of the TPP ylid nucleophilically attacks the carbonyl group on the substrate. (This forms a single bond between the TPP and the substrate.)
  2. The target bond on the substrate is broken, and its electrons are pushed towards the TPP. This creates a double bond between the substrate carbon and the TPP carbon and pushes the electrons in the N-C double bond in TPP entirely onto the nitrogen atom, reducing it from a positive to neutral form.
  3. In what is essentially the reverse of step two, the electrons push back in the opposite direction forming a new bond between the substrate carbon and another atom. (In the case of the decarboxylases, this creates a new carbon-hydrogen bond. In the case of transketolase, this attacks a new substrate molecule to form a new carbon-carbon bond.)
  4. In what is essentially the reverse of step one, the TPP-substrate bond is broken, reforming the TPP ylid and the substrate carbonyl.

TPP Mechanism.svg

The TPP thiazolium ring can be deprotonated at C2 to become an ylid:

TPP thiazolium.svg

A full view of TPP. The arrow indicates the acidic proton.

Thiamine pyrophosphate ng.png

See also

Related Research Articles

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The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of biochemical reactions to release the energy stored in nutrients through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. The chemical energy released is available under the form of ATP. The Krebs cycle is used by organisms that respire (as opposed to organisms that ferment) to generate energy, either by anaerobic respiration or aerobic respiration. In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, that are used in numerous other reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest components of metabolism. Even though it is branded as a "cycle", it is not necessary for metabolites to follow only one specific route; at least three alternative segments of the citric acid cycle have been recognized.

<span class="mw-page-title-main">Thiamine</span> Chemical compound

Thiamine, also known as thiamin and vitamin B1, is a vitamin, an essential micronutrient for humans and animals. It is found in food and commercially synthesized to be a dietary supplement or medication. Phosphorylated forms of thiamine are required for some metabolic reactions, including the breakdown of glucose and amino acids.

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Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is the first chemical step in photosynthesis, is called carboxylation, the addition of CO2 to a compound. Enzymes that catalyze decarboxylations are called decarboxylases or, the more formal term, carboxy-lyases (EC number 4.1.1).

<span class="mw-page-title-main">Pyruvate dehydrogenase complex</span> Three-enzyme complex

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An ylide or ylid is a neutral dipolar molecule containing a formally negatively charged atom (usually a carbanion) directly attached to a heteroatom with a formal positive charge (usually nitrogen, phosphorus or sulfur), and in which both atoms have full octets of electrons. The result can be viewed as a structure in which two adjacent atoms are connected by both a covalent and an ionic bond; normally written X+–Y. Ylides are thus 1,2-dipolar compounds, and a subclass of zwitterions. They appear in organic chemistry as reagents or reactive intermediates.

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<span class="mw-page-title-main">Isocitrate dehydrogenase</span> Class of enzymes

Isocitrate dehydrogenase (IDH) (EC 1.1.1.42) and (EC 1.1.1.41) is an enzyme that catalyzes the oxidative decarboxylation of isocitrate, producing alpha-ketoglutarate (α-ketoglutarate) and CO2. This is a two-step process, which involves oxidation of isocitrate (a secondary alcohol) to oxalosuccinate (a ketone), followed by the decarboxylation of the carboxyl group beta to the ketone, forming alpha-ketoglutarate. In humans, IDH exists in three isoforms: IDH3 catalyzes the third step of the citric acid cycle while converting NAD+ to NADH in the mitochondria. The isoforms IDH1 and IDH2 catalyze the same reaction outside the context of the citric acid cycle and use NADP+ as a cofactor instead of NAD+. They localize to the cytosol as well as the mitochondrion and peroxisome.

Thiazole, or 1,3-thiazole, is a 5-membered heterocyclic compound that contains both sulfur and nitrogen. The term 'thiazole' also refers to a large family of derivatives. Thiazole itself is a pale yellow liquid with a pyridine-like odor and the molecular formula C3H3NS. The thiazole ring is notable as a component of the vitamin thiamine (B1).

<span class="mw-page-title-main">Transketolase</span> Enzyme involved in metabolic pathways

Transketolase is an enzyme that, in humans, is encoded by the TKT gene. It participates in both the pentose phosphate pathway in all organisms and the Calvin cycle of photosynthesis. Transketolase catalyzes two important reactions, which operate in opposite directions in these two pathways. In the first reaction of the non-oxidative pentose phosphate pathway, the cofactor thiamine diphosphate accepts a 2-carbon fragment from a 5-carbon ketose (D-xylulose-5-P), then transfers this fragment to a 5-carbon aldose (D-ribose-5-P) to form a 7-carbon ketose (sedoheptulose-7-P). The abstraction of two carbons from D-xylulose-5-P yields the 3-carbon aldose glyceraldehyde-3-P. In the Calvin cycle, transketolase catalyzes the reverse reaction, the conversion of sedoheptulose-7-P and glyceraldehyde-3-P to pentoses, the aldose D-ribose-5-P and the ketose D-xylulose-5-P.

<span class="mw-page-title-main">Pyruvate decarboxylase</span> Class of enzymes

Pyruvate decarboxylase is an enzyme that catalyses the decarboxylation of pyruvic acid to acetaldehyde. It is also called 2-oxo-acid carboxylase, alpha-ketoacid carboxylase, and pyruvic decarboxylase. In anaerobic conditions, this enzyme participates in the fermentation process that occurs in yeast, especially of the genus Saccharomyces, to produce ethanol by fermentation. It is also present in some species of fish where it permits the fish to perform ethanol fermentation when oxygen is scarce. Pyruvate decarboxylase starts this process by converting pyruvate into acetaldehyde and carbon dioxide. Pyruvate decarboxylase depends on cofactors thiamine pyrophosphate (TPP) and magnesium. This enzyme should not be mistaken for the unrelated enzyme pyruvate dehydrogenase, an oxidoreductase, that catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA.

<span class="mw-page-title-main">Azomethine ylide</span>

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<span class="mw-page-title-main">Pyruvate dehydrogenase (lipoamide) alpha 1</span> Protein-coding gene in the species Homo sapiens

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<span class="mw-page-title-main">Pyruvate dehydrogenase (lipoamide) alpha 2</span> Protein-coding gene in the species Homo sapiens

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