Thiamin




B vitamins are complex, water-soluble organic chemicals, often containing heterocyclic ring systems (containing one or more atoms other than carbon atoms); they cannot be synthesized by humans and are, therefore, required nutrients. Each of these vitamins is converted by the body into a coenzyme. Coenzymes are cofactors essential to the catalytic activity of enzymes.

Thiamin is also known as vitamin B 1 . In the body it is converted to thiamin pyrophosphate (TPP), an essential coenzyme serving enzymes involved in the breakdown of nutrient molecules for energy. Thiamin deficiency in its severest form causes beriberi.

Thiamin is converted to TPP via the transfer of a pyrophosphate group to thiamin from adenosine triphosphate (ATP) .

In animals TPP-dependent decarboxylation reactions are essential to the production of energy needed for cell metabolism . In these reactions α -ketoacids are converted to acyl CoA molecules and carbon dioxide. The reactions (e.g., the conversion of pyruvate to acetyl CoA) are an important part of the breakdown of carbohydrates, and of the conversion of several classes of molecules (carbohydrates, fats, and proteins) to energy, carbon dioxide, and water in the citric acid cycle. In other organisms, in addition to its participation in the above reactions, TPP is a required coenzyme in alcohol fermentation, in the carbon fixation reactions of photosynthesis , and in the biosynthesis of the amino acids leucine and valine.

Major food sources of thiamin are fortified breads, cereals, pasta, whole grains (especially wheat germ), lean meats (especially pork and liver), fish, peanuts, dried beans, peas, and soybeans. Fruits and vegetables are not high in thiamin but are a significant source of thiamin if they are consumed in large enough amounts. The daily value (DV) of thiamin for adults is 1.5 milligrams (5.3 × 10 −5 ounces). Thiamin deficiency virtually does not occur in North America. Because thiamin is water-soluble and easily removed from the body there is no known toxicity.

Beriberi has been found in people who eat polished rice (with husks discarded) and few other foods, as thiamin is in the husks of grains. Beriberi is associated with damage to the nervous system, brain, heart, and blood vessels. It is fatal if not treated with adequate amounts of thiamin. Lesser deficiencies of thiamin lead to weakness and fatigue. These lesser deficiencies respond rapidly to thiamin unless they are complicated by another condition, for example, alcoholism.

CASIMIR FUNK (1884–1967)

Beriberi, a fatal disease, was prevalent at the turn of the nineteenth century among groups who ate large quantities of polished rice. Casimir Funk correctly theorized that the discarded polishings contained some nutrient for disease prevention. Funk isolated this item and called it a "vitamine," combining vite, meaning life, and amine.

—Valerie Borek

SEE ALSO Coenzyme .

Vivienne A. Whitworth

Bibliography

Nelson, David L., and Cox, Michael M. (2000). Lehninger Principles of Biochemistry , 3rd edition. New York: Worth Publishers.

Internet Resources

"Thiamin." Yahoo Health. Available from http://www.yahoo.com/health .

"Thiamin Deficiency and Dependency." Merck Manual of Diagnosis and Therapy. Available from http://www.merck.com/pubs/mmanual .



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