Transketolase, an enzyme of both the pentose phosphate pathway in animals and the Calvin cycle of photosynthesis, catalyzes two important reactions, which operate in opposite directions in these two pathways. In the first reaction of the pentose phosphate pathway, the cofactor thiamine diphosphate accepts a 2-carbon fragment from a 5-carbon ketose, then transfers this fragment to a 5-carbon aldose to form a 7-carbon ketose.
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- Transketolase, an enzyme of both the pentose phosphate pathway in animals and the Calvin cycle of photosynthesis, catalyzes two important reactions, which operate in opposite directions in these two pathways. In the first reaction of the pentose phosphate pathway, the cofactor thiamine diphosphate accepts a 2-carbon fragment from a 5-carbon ketose, then transfers this fragment to a 5-carbon aldose to form a 7-carbon ketose. 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. The second reaction catalyzed by transketolase in the pentose phosphate pathway involves the same thiamine diphosphate-mediated transfer of a 2-carbon fragment from D-xylulose-5-P to the aldose erythrose-4-phosphate, affording fructose 6-phosphate and glyceraldehyde-3-P. Again, in the Calvin cycle exactly the same reaction occurs, but in the opposite direction. Moreover, in the Calvin cycle this is the first reaction catalyzed by transketolase, rather than the second. In mammals, transketolase connects the pentose phosphate pathway to glycolysis, feeding excess sugar phosphates into the main carbohydrate metabolic pathways. Its presence is necessary for the production of NADPH, especially in tissues actively engaged in biosyntheses, such as fatty acid synthesis by the liver and mammary glands, and for steroid synthesis by the liver and adrenal glands. Thiamine diphosphate is an essential cofactor, along with calcium. Transketolase is abundantly expressed in the mammalian cornea by the stromal keratocytes and epithelial cells and is putatively considered one of the corneal crystallins.
- Transketolase (TK) ist der Name für Enzyme, die eine Ketolgruppe von Xylulose-5-phosphat auf ein Aldol übertragen, meist Ribose-5-phosphat. Dieser Reaktionsschritt, zusammen mit dem der Transaldolase, verbindet die Glykolyse mit dem Pentosephosphatweg. Transketolasen kommen in Bakterien, Pflanzen und Tieren vor. In Säugetieren haben sich mehrere Isoformen gebildet, wie beispielsweise Transketolase-like-1. Mutationen am TKT-Gen führen zum Mangel an Transketolase-Aktivität, was zusammen mit Mangel an ihrem Coenzym Thiamin (Vitamin B1) zum Wernicke-Korsakow-Syndrom bei Alkoholikern führt.
- La transchetolasi è un enzima appartenente alla classe delle transferasi, che catalizza le seguenti reazioni: xilulosio 5-fosfato + ribosio 5-fosfato ⇄ gliceraldeide 3-fosfato + sedoeptuloso 7-fosfato Trasferisce un frammento a due atomi di carbonio dallo xilulosio-5-fosfato al ribosio-5-fosfato. sedoeptulosio 7-fosfato + -gliceraldeide 3-fosfato ⇄ -ribosio 5-fosfato + -xilulosio 5-fosfato Trasferisce un frammento a due atomi di carbonio dallo xilulosio-5-fosfato all'eritrosio 4-fosfato. Queste reazioni sono due passaggi della via dei pentoso fosfati. L'enzima è una proteina tiaminadifosfato. Ha un'ampia specificità per entrambi i reagenti. e.g. converte l'idrossipiruvato e R-CHO in CO e R-CHOH-CO-CHOH. La transchetolasi di Alkaligenes faecalis mostra alta attività con l'-eritrosio come accettore.
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- Transketolase, an enzyme of both the pentose phosphate pathway in animals and the Calvin cycle of photosynthesis, catalyzes two important reactions, which operate in opposite directions in these two pathways. In the first reaction of the pentose phosphate pathway, the cofactor thiamine diphosphate accepts a 2-carbon fragment from a 5-carbon ketose, then transfers this fragment to a 5-carbon aldose to form a 7-carbon ketose.
- Transketolase (TK) ist der Name für Enzyme, die eine Ketolgruppe von Xylulose-5-phosphat auf ein Aldol übertragen, meist Ribose-5-phosphat. Dieser Reaktionsschritt, zusammen mit dem der Transaldolase, verbindet die Glykolyse mit dem Pentosephosphatweg. Transketolasen kommen in Bakterien, Pflanzen und Tieren vor. In Säugetieren haben sich mehrere Isoformen gebildet, wie beispielsweise Transketolase-like-1.
- La transchetolasi è un enzima appartenente alla classe delle transferasi, che catalizza le seguenti reazioni: xilulosio 5-fosfato + ribosio 5-fosfato ⇄ gliceraldeide 3-fosfato + sedoeptuloso 7-fosfato Trasferisce un frammento a due atomi di carbonio dallo xilulosio-5-fosfato al ribosio-5-fosfato. sedoeptulosio 7-fosfato + -gliceraldeide 3-fosfato ⇄ -ribosio 5-fosfato + -xilulosio 5-fosfato Trasferisce un frammento a due atomi di carbonio dallo xilulosio-5-fosfato all'eritrosio 4-fosfato.
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- Transketolase
- Transketolase
- Transchetolasi
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