Time-resolved OH → EH transition of the aberrant ba3 oxidase from Thermus thermophilus

The kinetics of single-electron injection into the oxidized nonrelaxed state (O-H -> E-H transition) of the aberrant ba(3) cytochrome oxidase from Thermus thermophilus, noted for its lowered efficiency of proton pumping, was investigated by time-resolved optical spectroscopy. Two main phases of intraprotein electron transfer were resolved. The first component (tau similar to 17 mu s) reflects oxidation of Cu-A and reduction of the heme groups (low-spin heme b and high-spin heme a(3) in a ratio close to 50:50). The subsequent component (tau similar to 420 mu s) includes reoxidation of both hemes by Cu-B. This is in significant contrast to the O-H -> E-H transition of the aa(3)-type cytochrome oxidase from Paracoccus denitrificans, where the fastest phase is exclusively due to transient reduction of the low-spin heme a, without electron equilibration with the binuclear center. On the other hand, the one-electron reduction of the relaxed O state in ba(3) oxidase was similar to that in aa(3) oxidase and only included rapid electron transfer from Cu-A to the low-spin heme b. This indicates a functional difference between the relaxed O and the pulsed O-H forms also in the ba(3) oxidase from T thermophilus. (C) 2009 Elsevier B.V. All rights reserved.