The cytochrome bc1 complex from Rhodovulum sulfidophilum is a dimer with six quinones per monomer and an additional 6-kDa component.
A highly active, large-scale preparation of cytochrome bc1 complex has been obtained from the photosynthetic purple bacterium Rhodovulum (Rhv.) sulfidophilum. It has been characterized using mass spectrometry, quinone and lipid analysis as well as inhibitor binding. About 35 mg of pure complex can be obtained from 1 g of membrane protein. EPR spectroscopy and optical titrations have been used to obtain the redox midpoint potentials of the cofactors. The Em-value of 310 mV for the Rieske protein is the most positive midpoint potential for this protein in a bc1 complex so far. The bc1 complex from Rhv. sulfidophilum is very stable and consists of three subunits and a 6-kDa polypeptide. The complex appears as a dimer in solution and contains six quinone molecules per monomer which are tightly bound. EPR spectroscopy shows that the Q(o) site is highly occupied. High detergent concentrations convert the complex into an inactive, monomeric form that has lost the Rieske protein as well as the quinones and the 6-kDa component.
Montoya
G
G
European Molecular Biology Laboratory, Structural Biology Programme, Heidelberg, Germany.
te Kaat
K
K
Rodgers
S
S
Nitschke
W
W
Sinning
I
I
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D003902:Detergents / Q000494:pharmacology; D019281:Dimerization; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D014450:Electron Transport Complex III / Q000037:antagonists & inhibitors / Q000737:chemistry*; D004795:Enzyme Stability; D007506:Iron-Sulfur Proteins / Q000737:chemistry; D008055:Lipids / Q000032:analysis; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D011809:Quinones / Q000737:chemistry*; D016992:Rhodobacter / Q000201:enzymology*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013056:Spectrophotometry, Ultraviolet
D001426:Bacterial Proteins; D003902:Detergents; D007506:Iron-Sulfur Proteins; D008055:Lipids; D011809:Quinones; C037989:Rieske iron-sulfur protein; D014450:Electron Transport Complex III