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Summary
Most biological oxygen consumption is carried out by membrane-integrated oxidases, which fall into three main classes. The heme-copper oxidases (HCOs) of mitochondria and many bacteria (1) have a binuclear active site that contains a heme and a copper atom. They achieve rapid, virtually complete reduction of oxygen to water. The alternative oxidases (AOXs) found in certain plants, fungi, and bacteria have a heme-free iron-iron reactive site (2) that confers nitric oxide–resistant respiration (3). The last class, the bacterial cytochrome bd–type oxidases (4), are found in many pathogenic bacteria and have a distinctive heme composition consisting of two hemes b and one heme d. On page 583 of this issue, Safarian et al. report the atomic-resolution structure of a cytochrome bd–type oxidase from Geobacillus thermodenitrificans (5). The structure will facilitate targeted and rational drug development against cytochrome bd–type oxidases.
