Cytochrome aa3-600, one of the principal respiratory oxidases from Bacillus subtilis, is a member of the heme-copper superfamily of oxygen reductases, and is a close homologue of the cytochrome bo3 ubiquinol oxidase from Escherichia coli, but uses menaquinol instead of ubiquinol as a substrate.The enzyme also pumps protons across the membrane bilayer, generating a proton motive force.
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