Elevated Proton Leak of the Intermediate OH in Cytochrome c Oxidase

AUTOR(ES)

Bloch, Dmitry A.

FONTE

The Biophysical Society

RESUMO

The kinetics of the formation and relaxation of transmembrane electric potential (Δψ) during the complete single turnover of CcO was studied in the bovine heart mitochondrial and the aa3-type Paracoccus denitrificans enzymes incorporated into proteoliposome membrane. The real-time Δψ kinetics was followed by the direct electrometry technique. The prompt oxidation of CcO and formation of the activated, oxidized (OH) state of the enzyme leaves the enzyme trapped in the open state that provides an internal leak for protons and thus facilitates dissipation of Δψ (τapp ≤ 0.5–0.8 s). By contrast, when the enzyme in the OH state is rapidly re-reduced by sequential electron delivery, Δψ dissipates much slower (τapp > 3 s). In P. denitrificans CcO proteoliposomes the accelerated Δψ dissipation is slowed down by a mutational block of the proton conductance through the D-, but not K-channel. We concluded that in contrast to the other intermediates the OH state of CcO is vulnerable to the elevated internal proton leak that proceeds via the D-channel.

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