Thiamin (Vitamin B1) structurally consists of 2 rings that are bridged together as shown below.
Figure 10.31 Structure of thiamin1
Since it was one of the original vitamins, (remember vitamine), it was originally named thiamine. The -e has since been dropped in its spelling. Thiamin is sensitive to heat, so prolonged heating causes the cleavage of thiamin between the 2 rings destroying its activity2.
Like most of the B vitamins, thiamin's primary function is as a cofactor for enzymes. It is not thiamin alone that serves as a cofactor but instead thiamin diphosphate (thiamin + 2 phosphates), which is more commonly referred to as thiamin pyrophosphate (TPP). The structure of thiamin pyrophosphate is shown below.
Figure 10.32 Structure of thiamin pyrophosphate (aka thiamin diphosphate)3
In plants, thiamin is found in its free form, but in animals, it is mostly thiamin pyrophosphate. These phosphates must be cleaved before thiamin is taken up into the enterocyte4.
Thiamin uptake and absorption is believed to be an efficient process that is passive when thiamin intake is high and active when thiamin intakes are low4. There are two thiamin transporters (THTR), THTR1 and THTR2, that are involved in thiamin uptake and absorption. THTR1 is found on the brush border and basolateral membrane, while THTR2 is only found on the brush border membrane as shown below5.
Figure 10.33 Thiamin uptake and absorption
Like most water-soluble vitamins there is little storage of thiamin.
References & Links
- Byrd-Bredbenner C, Moe G, Beshgetoor D, Berning J. (2009) Wardlaw's perspectives in nutrition. New York, NY: McGraw-Hill.
- Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.
- Said H, Mohammed Z. (2006) Intestinal absorption of water-soluble vitamins: An update. Curr Opin Gastroenterol 22(2): 140-146.