AHCY, also known as adenosylhomocysteinase isoform 1, is an enzyme that catalyzes the reversible hydrolysis of S-adenosylhomocysteine (AdoHcy) to adenosine (Ado) and L-homocysteine (Hcy). AdoHcy hydrolysis is a reversible reaction with an equilibrium favoring AdoHcy formation, but hydrolysis prevails under physiological conditions due to the rapid removal of adenosine and homocysteine. Thus, AHCY activity in mammals is directly related to homocysteine level, an independent risk factor for vascular disease. It also functions as a regulator of biological transmethylation by controlling the concentration of AdoHcy, a potent competitive inhibitor of all S-adenosyl-L-methionine methyltransferases. Recombinant human AHCY protein, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.