Open AccessThe cytochrome bc 1 complex from Rhodovulum sulfidophilum is a dimer with six quinones per monomer and an additional 6‐kDa component
Author(s) -
Montoya Guillermo,
Kaat Kai te,
Rodgers Simon,
Nitschke Wolfgang,
Sinning Irmgard
Publication year - 1999
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1327.1999.00094.x
Subject(s) - dimer , component (thermodynamics) , monomer , chemistry , cytochrome , crystallography , organic chemistry , physics , polymer , thermodynamics , enzyme
A highly active, large‐scale preparation of cytochrome bc 1 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 E m ‐value of 310 mV for the Rieske protein is the most positive midpoint potential for this protein in a bc 1 complex so far. The bc 1 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.