transketolase


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trans·ke·to·lase

(trans-kē'tō-lās), [MIM*606781]
A transferase bringing about the reversible interconversion of sedoheptulose 7-phosphate and d-glyceraldehyde 3-phosphate to produce d-ribose 5-phosphate and d-xylulose 5-phosphate, and also other similar reactions, such as hydroxypyruvate and an aldehyde into CO2 and an extended hydroxypyruvate; a part of the nonoxidative phase of the pentose phosphate pathway.
See also: transaldolase.
References in periodicals archive ?
Stitt, "A small decrease of plastid transketolase activity in antisense tobacco transformants has dramatic effects on photosynthesis and phenylpropanoid metabolism," Plant Cell, vol.
Mocali, "Enhanced proteolytic activities in culture fibroblasts of Alzheimer patients are revealed by peculiar transketolase alterations," Journal of the Neurological Sciences, vol.
However, posttranscriptional regulation appears to play a significant role in the expression of corneal crystallins aldehyde dehydrogenase IIIA1 (Aldh3a1) and transketolase (Tkt), which constitute roughly 50% and 10% of the water-soluble protein, respectively, and only about 1% each of the total mRNA in the adult cornea [31].
Thiamine and its dependent enzymes, transketolase (TK), pyruvate dehydrogenase, a-ketoglutarate dehydrogenase and the branched chain a-ketoglutarate dehydrogenase complex are involved in the maintenance of NADPH levels and carbohydrate metabolism in the cell8.
The enhanced expression of transketolase-like 1 (TLKL-1) protein--the only transketolase that is overexpressed in cancer--was shown to correlate with a more malignant RCC phenotype in a study by Langbein and colleagues.[sup.20] These investigators suggested that enhanced transketolase activity induces a shift toward anaerobic glycolysis and promotes growth advantage in hypoxic conditions, and, in particular, may select cells that are resistant to current anti-angiogenesis targeted treatment.[sup.21]
Transketolase plays a role in a chain of reactions called the pentose phosphate pathway, whereas PDH and KGDH are involved in glycolysis and the citric acid cycle.
Yellow color marked pathway is the pentose phosphate pathway; the number in parenthesis is the gene copy found in the genome; GalK: galactokinase (EC 2.71.6); GalE: UDP-glucose 4-epimerase (EC 5.1.3.2); GalT: UDP-glucose-hexose-1-phosphate uridylyltransferase (EC 2.7.7.12); GalU: UTP-glucose-1- phosphate uridylyltransferase (EC 2.7.79); PGM: phosphoglucomutase (EC 5.4.2.2); XI: xylose isomerase (EC 5.3.1.5); XK: xylulokinase (EC 2.71.17); AI: arabinose isomerase (EC 5.3.1.4); RK: ribulokinase (EC 2.71.16); RI: ribose 5-phosphate isomerase (EC 5.3.1.6); RPE: ribulose-phosphate 3-epimerase (EC 5.1.3.1); TKL: transketolase (EC 2.2.1.1); TAL: transaldolase (EC 2.2.1.2).
Pancreatic cancer cells utilize the nonoxidative transketolase (TK) enzyme pathway, incorporating carbon atoms from glucose to make ribose, the sugar that forms the backbone of RNA and DNA required for cancer cell proliferation and tumor metastasis.
* It activates a vital enzyme called transketolase, which converts toxic glucose-induced metabolites into harmless compounds.
These latter ORFs are not conserved among cycloviruses and show low partial homology to bacterial enzymes, NAD-dependent DNA ligase of Psychrobacter (ORF3), transketolase of Sinorhizobium (ORF4), and dTDP-D-glucose 4,6-dehydratase of Actinomyces (ORF5).
This may be done by the activation of reductive pentose phosphate pathway (PPP) by high-dose thiamine therapy that would increase transketolase (TK) activity and stimulate the conversion of glyceraldehyde-3-phosphate (GA3P) and fructose-6-phosphate (F6P) to ribose-5-phosphate (R5P), thus reducing the risk of the development of diabetic complications.
Transketolase occurs twice in the hexose monophosphate shunt and since this pathway occurs in erythrocytes it is used to test for biological evidence of thiamine deficiency (1).