Alcohol dehydrogenase monomer

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Human alcohol dehydrogenase, or ADH, is formed by two identical monomers. Each of these monomers contains 374 amino acid residues and has a molecular weight of 74,000 daltons. There are two distinct regions within the enzyme: an NAD+-binding domain and a catalytic domain. The NAD+-binding domain spans from residue number 176 to 318 and is characterized by a central beta-sheet composed of six strands, flanked on both sides by alpha helices. This domain is where NAD+ binds, specifically at the C-terminus of the beta-sheet. In contrast, the catalytic domain extends from residues 1 through 175 and from residue 319 to 374. Like the NAD+-binding domain, it also has an alpha/beta structure. The interface between these two domains forms a cleft that contains the active site where the enzymatic reaction takes place. The inter-domain interface is formed by two helices, one originating from each domain and crossing over each other. Each monomer within ADH contains two zinc ions (Zn++), with one being located at the catalytic site and essential for the enzyme's ability to catalyze reactions.