RATIONAL APPROACHES TO THE DESIGN OF MECHANISM-BASED INHIBITORS OF S-ADENOSYLHOMOCYSTEINE HYDROLASE

Crucial to the rational design of inhibitors of S-adenosyl-L-homocyste ine (AdoHcy) hydrolase was the elucidation of its mechanism of catalys is by Palmer and Abeles (J. Biol. Chem. 254, 1217-1226, 1979). This me chanism involves an NAD(+)-dependent oxidation (oxidative activity) of the 3'-hydroxyl group of AdoHcy followed by elimination of homocystei ne (Hey) to form 4',5'-didehydro-3'-keto-Ado. Addition of water at the 5'-position (hydrolytic activity) of this tightly bound intermediate followed by an NADH-dependent reduction results in the formation of ad enosine (Ado). Many inhibitors of this enzyme have been shown to serve as substrates [e.g., ns-2-trans-3-dihydroxycyclopent-4-en-1-yl)adenin e, DHCeA)] for the oxidative activity of AdoHcy hydrolase, affording t he 3'-keto-derivative (e.g., 3'-keto-DHCeA), which is tightly bound to the enzyme, and converting the enzyme from its active form (NAD(+)) t o its inactive form (NADH) (Type I mechanism-based inhibitors; Wolfe a nd Borchardt, J. Med. Chem. 34, 1521-1530, 1991). More recently, subst rates [e.g., )-5',6'-didehydro-6'-deoxy-6'-fluorohomoadenosine, EDDFHA ] for the hydrolytic activity of AdoHcy hydrolase have been identified by our laboratories. Identification of hydrolytic substrates affords a new strategy for the design of more potent and more specific inhibit ors of AdoHcy hydrolase.