A revised model of the active site of alternative oxidase

The plant mitochondrial protein alternative oxidase catalyses dioxygen depe ndent ubiquinol oxidation to yield ubiquinone and water. A structure of thi s protein has previously been proposed based on an assumed structural homol ogy to the di-iron carboxylate family of proteins. However, these authors s uggested the protein has a very different topology than the known structure s of di-iron carboxylate proteins. We have reexamined this model and based on comparison of recent sequences and structural data on di-iron carboxylat e proteins we present a new model of the alternative oxidase which allows p rediction of active site residues and a possible membrane binding motif. (C ) 1999 Federation of European Biochemical Societies.