Chapter 19: Electron Transport Chains in Oxygenic Cyanobacteria

Cyanobacteria (blue-green algae) are introduced here and discussed as the paradigmatic organisms of oxygenic (plant-type) photosynthesis and aerobic (mitochondrial-type) respiration in both bioenergetic, evolutionary and ecological respects. As the most important energy-conserving biological mechanisms, both photosynthesis and respiration crucially depend on the membrane-bound chemiosmotic electron transport principle. Within the framework of a generalized endosymbiont hypothesis, therefore, the term free-living protochloromitochondria seems to be most suitable for these prokaryotic plants, which are also rightly named the bioenergetic nonplus-ultra. Being ideal laboratory organisms for (biochemical and biophysical) photosynthesis research some thermophilic species among them have recently been used for detailed X-ray structural analysis of no less than three of the most important energy-converting electron transfer complexes of plant-type photosynthesis, viz., Photosystems II and I and the cytochrome b₆ f complex.