S-Adenosylhomocysteine Hydrolase

摘要

S-Adenosylhomocysteine hydrolase (AdoHcyase; EC 3.3.1.1) catalyzes the overall reversible reaction. AdoHcy + H2O yields Ado + Hcy. The enzymatic synthesis of AdoHcy starts with the oxidation of the 3'-OH of adenosine (Ado) by an enzyme-bound NAD. Interest has been focused on steps (7) and (8), particularly with respect to the possibility of the release of adenine during the irreversible inactivation of the enzyme by nucleoside analogs. This report presents a detailed discussion on the interaction of various nucleoside analogs with AdoHcyase, in particular with respect to the inhibition of the enzyme activity. There are three main categories of inhibitors for the enzyme: (1) competitive inhibitors; (2) irreversible and the pseudo-irreversible inactivators; and (3) mixed type inhibitors which consist of nucleosides that can inhibit competitively and/or irreversibly. AdoHcyase is a fascinating enzyme with kinetic anomalies. More interesting phenomena have yet to unfold, especially from the cell mutants with altered AdoHcyase activities.