Haem O can replace haem A in the active site of cytochrome c oxidase from thermophilic bacterium PS3

Abstract

Thermophilic bacterium PS3 cultured under slightly air-limited conditions showed a mitochondrion-like cytochrome pattern similar to that in vigorously aerated cells, but an o-type cytochrome replaced cytochrome a ₃ as the CO-binding centre. Cytochrome cao-type oxidase was purified from the cell membranes by almost the same procedure as used for cytochrome caa ₃. The turnover number of cytochrome cao was higher than that of cytochrome caa ₃, but the K _m's of the two enzymes for cytochrome c and O₂ were almost the same. Gel electrophoresis in the presence of sodium dodecyl sulfate gave bands of four subunits at the identical positions both for cytochrome cao and cytochrome caa ₃. Cytochrome cao contained a novel kind of haem in addition to haems C and A. This novel haem is likely to be haem O, very recently found as the chromophore of the cytochrome bo complex in Escherichia coli. These data suggest that cytochrome cao is an alternative form of cytochrome c oxidase (cytochrome caa ₃), in which the cytochrome a ₃ centre of the enzyme is replaced with cytochrome o.