The mitochondrial cytochromeb missense mutation, G167E, has been reported inapatientwithcardiomyopathy. The residue G167 is located in an extramembranous helix close to the hinge region of the iron–sulfur protein. In order to characterize the effects of the mutation on the structure and function of thebc1complex, we introducedG167E into the highly similar yeast cytochromeb. The mutation had a severe effect on the respiratory function, with the activity of thebc1complex decreased to a fewper cent of the wild type
