THE STRUCTURE OF THE MEMRANE PROTEIN QUINOL OXIDASE

Jeff Abramson, Gisela Larsson and So Iwata¹, Arturo Garcia-Horsman, Anne Puustinen and Marten Wikstrom²

¹Uppsala University, Department of Biochemistry
²University of Helsinki, Helsinki Bioenergtics Group, Department of Medical Chemistry

Ubiquinol oxidase is the terminal enzyme in the respiratory chain of Escherichia coli which catalyses the reduction of molecular oxygen to water using membrane bound ubiquinol and stores the energy liberated from this reaction as a proton gradient. We have obtained crystals of ubquinol oxidase that diffract better than 3.0 A. From the diffraction data, the space group has been determined to be C2221, with the cell dimensions of a= 92.1 A, b= 372.5A and c= 232.7A. There are two molecules in the asymmetric unit with a solvent content of 62 %. Molecular replacement studies, using a modified form of cytochrome c oxidase from Paracoccus denitrificans as a model, has been performed. The solution shows reasonable packing of the molecules and the calculated electron density revealed some new structural features of the quinol oxidase.