... Germany;2Department of Basic and Applied Biology, University of L’Aquila, ItalyIntroducing site-directed mutations in surface-exposedresidues of subunit II of the heme aa3cytochrome c oxidase of Paracoccus ... complex of therespiratory chains of mitochondria and many bacteria[1–4]. It catalyzes the reduction of oxygen to water, couplingthe free energy of this reaction to the generation of a protongradient ... of singlemutants in each of the two positions, or of double mutants,was generated (Table 1). While Kmvalues for all complexesdo not deviate from that of wild-type by more than a factorof...