|Benight, Nancy - BAYLOR COLLEGE MED|
|Stoll, Barbara - BAYLOR COLLEGE MED|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: April 1, 2008
Publication Date: January 20, 2010
Citation: Benight, N.M., Burrin, D.G., Stoll, B. 2009. Intestinal metabolism of sulfur amino acids. In: Masella, R., Mazza, G., editors. Glutathione and Sulfur Amino Acids in Human Health and Disease. New Jersey, NJ: Wiley & Sons, Inc. p. 47-72. Technical Abstract: The gastrointestinal tract (GIT) serves a key function in the digestion of dietary protein and absorption of amino acids. However, the GIT is also an important site of amino acid metabolism in the body. Methionine is an indispensable amino acid and must be supplied in the diet. In addition, considerable attention in recent years has been focused on homocysteine, a product of methionine transmethylation. Numerous clinical studies have shown that elevated plasma homocysteine levels are strongly associated with increased risk for several diseases, including atherosclerosis, Alzheimers disease, ischemic and hemorrhagic stroke, and most recently inflammatory bowel disease (IBD). However, another intermediate formed during the initial step in transmethylation of methionine is S-adenosylmethionine (SAM), which has been shown to play a pivotal role in hepatic injury, regeneration, and alcohol-induced liver cancer. As the major methyl-donor in the body, SAM also plays an integral role in the regulation of DNA methylation, which is an important epigenetic determinant of gene expression and has been implicated in the inverse relationship between folate status and various cancers, particularly colorectal cancer. Cysteine is considered semi-dispensable, as it can be synthesized by all tissues in the body via transmethylation of methionine, yet requires an adequate source of methionine and serine precursors. Cysteine is the essential constituent amino acid in the functional (CXXC) motif of the major cellular antioxidant families, including glutathione, glutaredoxins, thioredoxins, and peroxiredoxins. As such, the bioavailability of cysteine, derived from methionine transsulfuration, proteolysis or the diet, has a critical influence on cellular redox function and the susceptibility to oxidant stress. In this chapter, we will discuss the evidence for sulfur amino acid metabolism in the gastrointestinal tract (GIT) and its functional importance in health and disease.