S-(5'-Adenosyl)-L-methionine chloride (SAM) is a ubiquitous methyl donor involved in a wide variety of biological reactions, including those mediated by DNA and protein methyltransferases. The transfer of a methyl group from SAM to an acceptor produces S-adenosyl-L-homocysteine . SAM is also metabolized by SAM decarboxlase to give decarboxylated SAM, which is involved in the polyamine pathway that generates spermine. Chemical's SAM has been purified to remove all S-adenosylhomocysteine, a known inhibitor of most SAM-dependent methyltransferases which is commonly found in other commercially available SAM. In addition, 's SAM contains no S-methylthioadenosine, a common impurity which may act as a substrate in some assay formats, resulting in high background.