in food and water. Glutathione, an important antioxidant compound, is one of the more studied nonprotein organic sources of sulfate in the diet.
There are hundreds of sulfur-containing compounds in the human body, and the body synthesizes all of them, with the exception of the vitamins thiamin and biotin. Precursors include sulfate obtained from dietary intake and ingestion of the indispensable amino acids methionine and cysteine (cysteine is considered conditionally indispensable) (Shils et al., 1999).
One of the important roles for sulfate is in the biosynthesis of 3′-phosphoadenosine-5′-phosphosulfate (PAPS). Inorganic sulfate is required along with adenosine triphosphate. PAPS, also known as active sulfate, is used in the biosynthesis of many essential body compounds (Box 7-1), some of which are not absorbed intact when present in foods.
Gastrointestinal absorption of sulfate can occur in the stomach, small intestine, and colon (Anast et al., 1965; Batt, 1969; Cardin and Mason, 1975, 1976; Cole and Evrovski, 2000; Kandylis, 1983; Kaneko-Mohammed and Hogben, 1964). Absorption is a sodium-dependent active process (Ahearn and Murer, 1984; Florin et al., 1991; Langridge-Smith et al., 1983). When soluble sulfate salts (e.g., potassium sulfate or sodium sulfate) are consumed, more than 80 percent of oral sulfate doses are absorbed, as shown by isotopic tracer studies (Bauer, 1976; Florin et al., 1991).
With insoluble sulfate salts, such as barium sulfate, almost no absorption occurs (Ahmed and Hamza, 1989). When magnesium sul-
BOX 7-1 Examples of Compounds Biosynthesized Using 3′-Phosphoadenosine-5′-Phosphosulfate