Abstract
Cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase EC 1.9.3.1) was purified from thermophilic bacterium PS3 by ion-exchange and hydroxyapatite chromatography in the presence of Triton X-100. The enzyme possessed 15.9 nmol heme a, 8.9 nmol heme c and 16–18 ng atom Cu per mg protein and was composed of three subunits of relative molecular mass 56000, 38000 (heme c-binding) and 22000. Since the ratio of the subunits was 1:1:1, one enzyme unit may be composed of one molecule each of the three subunits containing two hemes a, one heme c and two copper atoms. The enzyme shows very similar absorption characteristics, including the CO difference spectrum, to the mitochondrial enzyme, indicating that the PS3 enzyme is of the cytochrome aa 3 type with a firmly bound cytochrome c. The enzyme rapidly oxidizes cytochrome c-551 from PS3 and cytochrome c-552 from Thermus thermophilus, and has a lower affinity for yeast cytochrome c from Candida krusei. The reduction product of oxygen is concluded to be water on the basis of stoichiometric measurements. The enzyme, when reconstituted into proteoliposomes, can translocate H + in an uncoupler-sensitive fashion, indicating that the enzyme is a proton pump.
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