Detergent-solubilized Escherichia coli cytochrome bo(3) ubiquinol oxidase:a monomeric, not a dimeric complex

The protein molecular weight, M-r, and hydrodynamic radius, R-s, of Triton X-100-solubilized Escherichia coli cytochrome bos were evaluated by compute r fitting of sedimentation velocity data,vith finite element solutions to t he Lamm equation. Detergent-solubilized cytochrome bo(3) sediments as a hom ogeneous species with an s(20,w) Of 6.75 s and a D-20,D-w of 3.71 x 10(-7) cm(2)/s, corresponding to a R-s of 5.8 nm and a M-r of 144 000 +/- 3500, Th e protein molecular weight agrees very well with the value of 143 929 calcu lated from the four known subunit sequences and the value of 143 025 measur ed by MALDI mass spectrometry for the histidine-tagged enzyme. We conclude that detergent-solubilized E. coli ubiquinol oxidase is a monomeric complex of the four known subunits, (C) 1999 Federation of European Biochemical So cieties.