Transketolase activity

Early studies showed that the development of neurological abnormalities in thiamin deficiency did not follow the same time course as the impairment of pyruvate and 2-oxoglutarate dehydrogenase or transketolase activities. The brain regions in which metabolic disturbances are most marked were not those that are vulnerable to anatomical lesions. These studies suggested a function for thiamin in the nervous system other than its coenzyme role. 

On the basis of depletion/repletion studies, an intake ofO.2 mgper 1,000kcal is required to maintain normal urinary excretion, but an intake of 0.3 mg per 1,000 kcal is required for a normal transketolase activation coefficient. At low levels of energy intake, there will be a requirement for metabolism of endogenous substrates and to maintain nervous system thiamin triphosphate. 

Measurement of red ceil transketolase activity can be used as an index of thiamine deficiency. 

These various reports stress the need to supplement parenteral nutrition with thiamine-containing vitamins unless there is adequate dietary intake, and to monitor serum thiamine and erythrocyte transketolase activity so that supplementary thiamine can be given in good time, if necessary intravenously (45). Giving thiamine will not rectify the various disorders if hepatic function is severely disturbed, because then thiamine is not phosphorylated and hence remains physiologically inactive. 

The most commonly used enzyme for the functional assay is transketolase. Transketolase catalyzes two reactions in the pentose phosphate pathway (Figure 30-10). As an enzyme within the erythrocyte, transketolase is independent of nonspecific changes in the extracellular plasma. As vitamin Bi deficiency becomes more severe, (1) thiamine becomes limiting in the body cells, (2) the amount of the coenzyme is depleted, and (3) the transketolase activity sub-... 

The transketolase activation test is in reality two tests one a measurement of basal activity and the other the degree to which the basal activity can be increased by exogenous thiamine pyrophosphate, and each may be influenced by different factors. There is evidence that chronic deficiency states of thiamine may down regulate synthesis of the apoen-zyme. In comparison studies against erythrocyte TPP concentrations, better correlations were obtained with basal activity rather than the activation coefficient. ... 

Baines M, Davies G. The evaluation of erythrocyte thiamin diphosphate as an indicator of thiamin status in man, and its comparison with erythrocyte transketolase activity measurements. Ann Clin Biochem 1988 25 (Pt 6) 698-705. 

FenneUy J, Frank O, Baker H, Leevy CM. Red blood cell-transketolase activity in malnourished alcoholics with cirrhosis. Am J Clin Nutr 1967 20 946-9. 

Puxty JA, Haskew AE, Ratcliffe JG, McMurray J. Changes in erythrocyte transketolase activity and the thiamine pyrophosphate effect during storage of blood. Ann Clin Biochem 1985 22 (Pt 4) 423-7. 

Talwar D, Davidson H, Cooney J, St JO Reilly D. Vitamin B(l) status assessed by direct measurement of thiamin pyrophosphate in erythrocytes or whole blood by HPLC comparison with erythrocyte transketolase activation assay. Clin Chem 2000 46 704-10. 

Thiamine deficiency can be assessed by measuring blood levels. Increased blood levels of pyruvate and lactate suggest thiamine deficiency. Measurement of erythrocyte transketolase activity, which requires TPP as a coenzyme, confirms the deficiency. 

Thiamine deficiency is most frequently assessed by assaying erythrocyte transketolase activity in the presence and absence of added TPP. If the red blood cells have sufficient thiamine, the transketolase will be fully saturated with TPP, and no increase in activity will be observed when TPP is added to the assay system. An increase in transketolase activity indicates that the patient is thiamine deficient. 

B, (Thiamin) Beri-Beri Plasma levels or RBC transketolase activation... 

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