ROTENONE-INSENSITIVE INTERNAL NADH-QUINONE OXIDOREDUCTASE OF SACCHAROMYCES-CEREVISIAE MITOCHONDRIA - THE ENZYME EXPRESSED IN ESCHERICHIA-COLI ACTS AS A MEMBER OF THE RESPIRATORY-CHAIN IN THE HOST-CELLS

The NDI1 gene encodes the internal rotenone-insensitive NADH-quinone o xidoreductase localized in the inner mitochondrial membranes of Saccha romyces cerevisiae. The T7 tag-fused mature NDI1 was overexpressed in Escherichia coli. The overexpressed NDI1 was exclusively found in the membrane fraction. The NDI1-overexpressed membranes showed significant ly increased activities of NADH oxidase and NADH-ubiquinone-1 (UQ(1)) reductase when compared with the control membranes. Flavone, which is a specific inhibitor of the S, cerevisiae NDI1, inhibited almost compl etely NADH oxidase and NADH-UQ(1) reductase activities of NDI1-overexp ressed membranes but scarcely inhibited these activities of the contro l membranes. In addition, the NADH oxidase activity of the NDI1-overex pressed membranes was also inhibited by KCN as well as the control mem branes. These results indicate that the overexpressed NDI1 worked as a member of the respiratory chain in the host cells, even though E. col i membranes are different from S. cerevisiae inner mitochondrial membr anes in terms of quinones and lipid composition. (C) 1998 Federation o f European Biochemical Societies.