Understanding the Cytochrome bc Complexes By What They Don't Do. The Q-cycle at 30.
The cytochrome (cyt) bc1 and b6?f complexes are central components of the respiratory and photosynthetic electron transport chains. These complexes carry out an extraordinary sequence of electron and proton transfer reactions that conserve redox energy in the form of a trans-membrane proton motive force for use in synthesizing ATP and other processes. Thirty years ago, Peter Mitchell proposed a general turnover mechanism for these complexes, which he called the Q-cycle. Since that time, many opposing schemes have challenged the Q-cycle, but with the accumulation of large amounts of biochemical, kinetic, thermodynamic and high-resolution structural data, the Q-cycle has triumphed as the accepted model although some of the intermediate steps are poorly understood and still controversial. Perhaps the major research questions concerning the cyt bc1 and b6f complexes now surround how the enzymes suppress deleterious and dissipative side reactions. In particular, most Q-cycle models involve reactive semiquinone radical intermediates which can reduce O2 to superoxide, and can lead to cellular oxidative stress. Interestingly, each of the current models to explain the avoidance of side reactions involves unprecedented or unusual enzyme mechanisms the testing of which will involve cutting edge theory and experimental approaches.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 878254
- Report Number(s):
- PNWD-SA-7038; 2358; TRN: US0602288
- Journal Information:
- Trends in Plant Science, Vol. 11, Issue 1
- Country of Publication:
- United States
- Language:
- English
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