Fig. 4. A proposed catalytic cycle of CDH including domain-flipping motions. (i) The resting form of CDH (DHoxCYTox) binds cellobiose and then transfer of two-electrons from cellobiose to the FAD cofactor results in the generation of DHredCYTox and cellobiono-1,5-lactone as the product; (ii) one-electron IET from reduced FAD to ferric heme (DHsqCYTred) occurs, which has been proposed to represent the rate-limiting step in the cycle;17,34,35 (iii) the reduced CYT domain in DHsqCYTred subsequently transfers one electron to an external electron acceptor, leading to the generation of DHsqCYTox; (iv) second IET occurs from one-electron reduced FAD to ferric heme to produce DHoxCYTred; and (v) the reduced CYT domain transfers another electron to the external electron acceptor to regenerate the resting form.
