Transketolases beriberi

B, Thiamin Coenzyme in pyruvate and a-ketoglutarate, dehydrogenases, and transketolase poorly defined function in nerve conduction Peripheral nerve damage (beriberi) or central nervous system lesions (Wernicke-Korsakoff syndrome)... 

Vitamin B1 (thiamine) has the active form, thiamine pyrophosphate. It is a cofactor of enzymes catalyzing the conversion of pyruvate to acetyl CoA, a-ketoglutarate to succinyl CoA, and the transketolase reactions in the pentose phosphate pathway. A deficiency of thiamine causes beriberi, with symptoms of tachycardia, vomiting, and convulsions. In Wernicke-Korsakoff syndrome (most common in alcoholics), individuals suffer from apa thy, loss of memory, and eye movements. There is no known toxicity for this vitamin. 

As there are no reports of adverse effects from consumption of excess thiamine from food and supplements (supplements of 50 mg/day are widely available without prescription), and the data are inadequate for a quantitative risk assessment, no UL has been defined for thiamine. However, as stimulators of transketolase enzyme synthesis such as thiamine support a high rate of nucleic acid ribose synthesis necessary for tumor cell survival, chemotherapy resistance, and proliferation, some concern has been expressed that thiamine supplementation of common food products may contribute to increased cancer rates in the Western world. There is, however, littie evidence to support this assumption. Rarely, individuals given high-dose intravenous thiamine in treatment of beriberi have developed anaphylaxis, the frequency being about 1 100,000. 

Beriberi is associated with low transketolase activity in the blood, and determination of transketolase activity may be a helpful diagnostic tool in detecting mild forms of thiamine deficiencies. The fact that adding thiamine pyrophosphate to the system restores transketolase activity confers specificity to this procedure. Although the decrease in transketolase activity is easy to explain in view of the role that thiamine plays in that reaction, the mechanism of the alteration in adenosine-5 -phosphatase is not so obvious. The total activity is decreased despite a slight increase of adenosine phosphatase in the nuclei, and the decrease in total activity results from a marked decrease of adenosine phosphatase in the fibers. Increased thiamine pyrophosphate and alkaline phosphatase have also been observed in the optic tectum of the deficient chicken, but these changes remain unexplained. 

Kuriyama, M., Yokomine, R., Arima, H., Hamada, R., and Igata, A., 1980. Blood vitamin Bl, transketolase and thiamine pyrophosphate (TPP) effect in beriberi patients, with studies employing discriminant analysis. Clinica Chimica Acta. 108 159-168. 

Beriberi is caused by a deficiency of thiamin (also called thiamine, aneurin(e), and vitamin Bj). Classic overt thiamin deficiency causes cardiovascular, cerebral, and peripheral neurological impairment and lactic acidosis. The disease emerged in epidemic proportions at the end of the nineteenth century in Asian and Southeast Asian countries. Its appearance coincided with the introduction of the roller mills that enabled white rice to be produced at a price that poor people could afford. Unfortunately, milled rice is particularly poor in thiamin thus, for people for whom food was almost entirely rice, there was a high risk of deficiency and mortality from beriberi. Outbreaks of acute cardiac beriberi still occur, but usually among people who live under restricted conditions. The major concern today is subclinical deficiencies in patients with trauma or among the elderly. There is also a particular form of clinical beriberi that occurs in patients who abuse alcohol, known as the Wer-nicke-Korsakoff syndrome. Subclinical deficiency may be revealed by reduced blood and urinary thiamin levels, elevated blood pyruvate/lactate concentrations and a-ketoglutarate activity, and decreased erythrocyte transketolase (ETKL) activity. Currently, the in vitro stimulation of ETKL activity by thiamin diphosphate (TDP) is the most useful functional test of thiamin status where an acute deficiency state may have occurred. The stimulation is measured as the TDP effect. 

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