Crystallization of cytochrome bc1 complex

Abstract

Complex III (cytochrome bc1 particle; ubiquinol:ferricytochrome c oxidoreductase, EC 1.10.2.2) was purified from beef heart mitochondria by a combination of hydrophobic interaction and affinity chromatography. By washing the complex with detergent on the hydrophobic interaction column, phospholipids were effectively depleted; 7 mol of cardiolipin per mol of cytochrome c1 was retained in the final sample. NaDodSO4 gel electrophoresis showed nine polypeptide subunits in the sample. The molecular weight of the complex was estimated to be approximately equal to 225,000 from the specific heme c1 content and the subunit composition. The purified complex was crystallized by slow removal of the detergent in which the complex was dispersed. Electron micrographs and electron diffraction patterns showed that the crystal is hexagonal with unit cell dimensions a = b = 113 A, c = 132 A, and with angles alpha = beta = 90 degrees, gamma = 120 degrees. The role of bound cardiolipin in the structural integrity of the complex was discussed.