Detergent-solubilized Escherichia coli cytochrome bo3 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 bo3 were evaluated by computer fitting of sedimentation velocity data with finite element solutions to the Lamm equation. Detergent-solubilized cytochrome bo3 sediments as a homogeneous species with an S20,w of 6.75 s and a D20,w of 3.71 x 10(-7) cm2/s, corresponding to a R(s) of 5.8 nm and a M(r) of 144,000 +/- 3500. The protein molecular weight agrees very well with the value of 143,929 calculated from the four known subunit sequences and the value of 143,025 measured 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.