Sulfation of drugs and xenobiotics is catalyzed by cytosolic sulfotransferases (SULTs, EC 2.8.1) that utilize the cofactor 3'-phosphoadenosine 5'-phosphosulfate (PAPS).128 Membrane-bound forms of the enzyme are known which sulfate heparins, tyrosines in proteins, and proteoglycans, but these enzymes have little or no activity toward drugs. The reactivity of cytosolic SULTs overlaps with the UGTs, but the substrate range is not as diverse. SULTs are mostly active with phenols, alcohols, and arylamines, but many endogenous substrates are also recognized, e.g., steroids, bile acids, neurotransmitters, and carbohydrates. As with the glucuronidation, sulfation reactions usually result in more polar species that are readily excreted in the urine. However, SULTs are also implicated in toxicological reactions if nonenzymatic loss of SO4_ occurs to generate a relatively stable carbocation, e.g., from N-arylamines and benzylic alcohols, that can react with proteins and DNA.129
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WHAT IT IS A three-phase plan that has been likened to the low-carbohydrate Atkins program because during the first two weeks, South Beach eliminates most carbs, including bread, pasta, potatoes, fruit and most dairy products. In PHASE 2, healthy carbs, including most fruits, whole grains and dairy products are gradually reintroduced, but processed carbs such as bagels, cookies, cornflakes, regular pasta and rice cakes remain on the list of foods to avoid or eat rarely.