Disposition of Endogenous S-Adenosylhomocysteine and Homocysteine Following Exposure to Nucleoside Analogues and Methotrexate
S-Adenosylhomocysteine (AdoHcy) is a product from and an inhibitor of S-adenosylmethionine-dependent transmethylation reactions. This compound is degraded to adenosine and L-homocysteine (Hcy) in the cell through the action of the enzyme AdoHcy hydrolase (EC 126.96.36.199.) (de la Haba & Cantoni, 1959). The view is held that the AdoHcy hydrolase reaction is the only source of Hcy in vertebrates (Cantoni & Chiang, 1980). Hcy is converted to cystathionine or is salvaged to methionine. In all tissues, except liver and kidney, the latter pathway is catalyzed by a single enzyme, which requires 5-methyl -tetrahydrofolate as methyl donor (Mudd & Levy, 1983). These metabolic relations are depicted in figure 1.
KeywordsAdenosine Methotrexate Folate Methionine Homocysteine
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