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Thiamine pyrophosphate is a cofactor that is present in all living systems, in which it catalyzes several biochemical reactions. 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 ...
It serves as a riboswitch [1] [2] that binds thiamine pyrophosphate (TPP) directly and modulates gene expression through a variety of mechanisms in archaea, bacteria and eukaryotes. [3] [4] [5] TPP is the active form of thiamine (vitamin B 1), an essential coenzyme synthesised by coupling of pyrimidine and thiazole moieties in bacteria.
While its role is well-known, the non-coenzyme action of thiamine and derivatives may be realized through binding to proteins which do not use that mechanism. [22] No physiological role is known for the monophosphate except as an intermediate in cellular conversion of thiamine to the di- and triphosphates.
[5] [9] [10] Mechanisms of the transformations are unknown. In Salmonella, HMP-P can be derived independently of purine biogenesis when AICAR is available. [11] [12] In algae, thiamine forms and precursors are scavenged by uptake from water of exogenous products from other organisms. In higher plants, thiamine biogenesis resembles that of bacteria.
Dihydrolipoyl transacetylase mechanism. Pyruvate decarboxylation requires a few cofactors in addition to the enzymes that make up the complex. The first is thiamine pyrophosphate (TPP), which is used by pyruvate dehydrogenase to oxidize pyruvate and to form a hydroxyethyl-TPP intermediate. This intermediate is taken up by dihydrolipoyl ...
A deficiency in any of the enzymes of this complex as well as an inhibition of the complex as a whole leads to a buildup of branched-chain amino acids and their harmful derivatives in the body. These accumulations lend a sweet smell to bodily excretions (such as ear wax and urine), leading to a pathology known as maple syrup urine disease .
Simplified mechanism for pyruvate dehydrogenase reaction. The TPP coenzyme is shown with abbreviated substituents. The thiamine pyrophosphate (TPP) converts to an ylide by deprotonation. The ylide attack the ketone group of pyruvate. The resulting adduct decarboxylates. The resulting 1,3-dipole reductively acetylates lipoamide-E2. [2]
Members of this protein family have been assigned as thiamine transporters by a phylogenomic analysis of families of genes regulated by the THI element, a broadly conserved RNA secondary structure element through which thiamine pyrophosphate (TPP) levels can regulate transcription of many genes related to thiamine transport, salvage, and de novo biosynthesis.