The 2 primary dietary forms of biotin are free biotin and biocytin (aka biotinyllysine)1. The structure of biotin is shown below.
Figure 10.81 Structure of biotin2
Biocytin is biotin bound to lysine as seen in its structure below.
Figure 10.82 Structure of biocytin3
Free biotin is believed to be highly absorbed. Before uptake, biocytin is acted on by the enzyme biotinidase, forming free biotin and lysine. Free biotin is then taken up into the enterocyte through the sodium-dependent multivitamin transporter (SMVT), as shown below1,4,5.
Figure 10.83 Free biotin is taken up into the enterocyte by the SMVT.
Most biotin is excreted in the urine.
References & Links
- 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.
- Zempleni J, Wijeratne SSK, Hassan Y. (2009) Biotin. Biofactors 35(1): 36-46.