Vitamin B1 (Thiamine) FUNCTION

Coenzyme function

Thiamin pyrophosphate (TPP) is a required coenzyme for a small number of very important enzymes. The synthesis of TPP from free thiamin requires magnesium, adenosine triphosphate (ATP), and the enzyme, thiamin pyrophosphokinase.

Pyruvate dehydrogenase, a-ketoglutarate dehydrogenase, and branched chain ketoacid (BCKA) dehydrogenase each comprise a different enzyme complex found within cellular organelles called mitochondria. They catalyze the decarboxylation of pyruvate, a-ketoglutarate, and branched-chain amino acids to form acetyl-coenzyme A, succinyl-coenzyme A, and derivatives of branched chain amino acids, respectively, all of which play critical roles in the production of energy from food. In addition to the thiamin coenzyme (TPP), each dehydrogenase complex requires a niacin-containing coenzyme (NAD), a riboflavin-containing coenzyme (FAD), and lipoic acid.

Transketolase catalyzes critical reactions in another metabolic pathway known as the pentose phosphate pathway. One of the most important intermediates of this pathway is ribose-5-phosphate, a phosphorylated 5-carbon sugar, required for the synthesis of the high-energy ribonucleotides, ATP and guanosine triphosphate (GTP), the nucleic acids, DNA and RNA, and the niacin-containing coenzyme NADPH, which is essential for a number of biosynthetic reactions. Because transketolase decreases early in thiamin deficiency, measurement of its activity in red blood cells has been used to assess thiamin nutritional status.

Non-coenzyme function

Thiamin triphosphate (TTP) is concentrated in nerve and muscle cells. Research in animals indicates that TTP activates membrane ion channels, possibly by phosphorylating them. The flow of electrolytes like sodium or potassium in or out of nerve and muscle cells through membrane ion channels plays a role in nerve impulse conduction and voluntary muscle action. Impaired formation of TTP may play a role in the neurologic symptoms of severe thiamin deficiency.