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Journal of Bacteriology, February 2002, p. 840-845, Vol. 184, No. 3
0021-9193/01/$04.00+0     DOI: 10.1128/JB.184.3.840-845.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Cytochrome aa₃ in Haloferax volcanii

Mikiei Tanaka,^* Naohide Ogawa, Kunio Ihara,^, Yasuo Sugiyama,^, and Yasuo Mukohata^,

Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan

Received 27 March 2001/ Accepted 21 September 2001

A cytochrome in an extremely halophilic archaeon, Haloferax volcanii, was purified to homogeneity. This protein displayed a redox difference spectrum that is characteristic of a-type cytochromes and a CN^- complex spectrum that indicates the presence of heme a and heme a₃. This cytochrome aa₃ consisted of 44- and 35-kDa subunits. The amino acid sequence of the 44-kDa subunit was similar to that of the heme-copper oxidase subunit I, and critical amino acid residues for metal binding, such as histidines, were highly conserved. The reduced cytochrome c partially purified from the bacterial membrane fraction was oxidized by the cytochrome aa₃, providing physiological evidence for electron transfer from cytochrome c to cytochrome aa₃ in archaea.

Present address: Center for Gene Research, Nagoya University, Nagoya 464-8602, Japan.

Present address: Department of Environmental Systems Engineering, Kochi University of Technology, Tosayamada, Kochi 782-8502, Japan.