    1.2.1.39 | More |
the oligomerization domains of all four subunits form the core of PADH and are responsible not only for the effective dimerization observed within the homotetramer, but also for the association of these dimers to form the tetramer. Each 496 amino acid PADH subunit consists of three domains: an N-terminal NADþ-binding domain (residues 1-130 and 159-269), a catalytic domain (residues 270-471), and an oligomerization domain (131-158 and 472-496). The enzyme has a unique set of intersubunit interactions and active site tunnel for substrate entrance. Each oligomerization domain of NPADH contains a six-residue insertion that extends this loop over the substrate entrance tunnel of a neighboring subunit, thereby obstructing the active site of the adjacent subunit. This feature might be an important factor in the homotropic activation and product inhibition mechanisms. The substrate channel of NPADH is narrower and lined with more aromatic residues, which include Phe170, Phe295, Phe466, and Trp177, suggesting a means for enhancing substrate specificity |
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