Transketolase

[Bred]

Transketolase, an enzyme of the Calvin cycle of photosynthesis, catalyzes the transfer of a 2-carbon fragment from a 5-carbon keto sugar (D-xyulose-5-P) to a 5-carbon aldo sugar (D-ribose-5-P) to form a 7-carbon keto sugar (sedoheptulose-7-P) and a 3-carbon aldo sugar (glyceraldehyde-3-P).

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 by the brain. Thiamine is an essential cofactor, along with calcium.

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Diagnostic use
Red cell transketolase activity is reduced in deficiency of thiamine (vitamin B1), and may be used in the diagnosis of Wernicke's encephalopathy and other B1-deficiency syndromes if the diagnosis is in doubt.[1] Apart from the baseline enzyme activity (which may be normal even in deficiency states), acceleration of enzyme activity after the addition of thiamine pyrophosphate may be diagnostic of thiamine deficiency (0-15% normal, 15-25% deficiency, >25% severe deficiency).[2]

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References
^ Smeets EHJ, Muller A, de Wael J. A NADH-dependent transketolase assay in erythrocyte hemolysates. Clin Chim Acta 1971;33:379–386. PMID 4330339.
^ Doolman R, Dinbar A, Sela B. Improved measurement of transketolase activity in the assessment of TPP effect. Eur J Clin Chem Clin Biochem 1995;33:445–446. PMID 7548453.
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