Analyzing your complexes: structure of the quinol-fumarate reductase respiratory complex.

The integral membrane protein complex quinol-fumarate reductase catalyzes the terminal step of a major anaerobic respiratory pathway. The homologous enzyme succinate-quinone oxidoreductase participates in aerobic respiration both as complex II and as a member of the Krebs cycle. Last year, two structures of quinol-fumarate reductases were reported. These structures revealed the cofactor organization linking the fumarate and quinol sites, and showed a cofactor arrangement across the membrane that is suggestive of a possible energy coupling function.