Ubihydroquinone: cytochrome (cyt) c oxidoreductase, or cyt bc1, is a widespread, membrane integral enzyme that plays a crucial role during photosynthesis and respiration. It is one of the major contributors of the electrochemical proton gradient, which is subsequently used for ATP synthesis. The simplest form of the cyt bc1 is found in bacteria, and it contains only the three ubiquitously conserved catalytic subunits: the FeS protein, cyt b and cyt c1. Here we present a preliminary X-ray structure of Rhodobacter capsulatus cyt bc1 at 3.8 Angstrom, and compare it to the available structures of its homologues from mitochondria and chloroplast. Using the bacterial enzyme structure, we highlight the structural similarities and differences that are found among the three catalytic subunits between the the different members of this family of enzymes. In addition, we discuss the locations of currently known critical mutations, and their implications in terms of the cyt bc1 catalysis.