Detergent modulation of electron and proton transfer reactions in bovine cytochrome c oxidase

The effect of detergents on electron and proton transfer in bovine cytochrome c oxidase was studied using steady-state and transient-state methods. Cytochrome c oxidase in lauryl maltoside has high maximal turnover (TNmax=400 s−1), whereas activity is low (TNmax=10 s−1) in Triton X-100. Single turnover studies of intramolecular electron transfer show similar rates in either detergent. Transient proton uptake experiments show the oxidase in lauryl maltoside consumes 1.8±0.3 H+/aa3 during either partial reduction of the oxidase or reaction of fully reduced enzyme with O2. However, the oxidase in Triton X-100 consumes 2.6±0.4 H+/aa3 during partial reduction and 1.0±0.2 H+/aa3 in the O2 reaction. Absorption spectra recorded during turnover show that the enzyme undergoes activation in lauryl maltoside, but does not activate in Triton X-100. We propose that cytochrome c oxidase in different detergents allows access to different sites of protonation, which in turn influences steady-state activity.