The mechanism for oxygen reduction in the C family cbb3 cytochrome c oxidases - Implications for the proton pumping stoichiometry.

The mechanism for oxygen reduction in the C family cbb3 cytochrome c oxidases - Implications for the proton pumping stoichiometry.
J Inorg Biochem. 2019 Oct 31;203:110866
Authors: Blomberg MRA
Abstract
Cytochrome c oxidases (CcOs) couple the exergonic reduction of molecular oxygen to proton pumping across the membrane in which they are embedded, thereby conserving a significant part of the free energy. The A family CcOs are known to pump four protons per oxygen molecule, while there is no consensus regarding the proton pumping stoichiometry for the C family cbb3 oxidases. Hybrid density functional theory is used here to investigate the catalytic mechanism for oxygen reduction in cbb3 oxidases. A surprising result is that the barrier for O O bond cleavage at the mixed valence reduction level seems to be too high compared to the overall reaction rate of the enzyme. It is therefore suggested that the O O bond is cleaved only after the first proton coupled reduction step, and that this reduction step most likely is not coupled to proton pumping. Furthermore, since the cbb3 oxidases have only one proton channel leading to the active site, it is proposed that the activated EH intermediate, suggested to be responsible for proton pumping in one of the reduction steps in the A family, cannot be involved in the catalytic cycle for cbb3, which results in the lack of proton pumping also in the E to R reduction step. In summary, the calculations ...

Source: Journal of Inorganic Biochemistry - October 30, 2019 Category: Biochemistry Authors: Blomberg MRA Tags: J Inorg Biochem Source Type: research