Co-existence of photosynthetic and respiratory activities in cyanobacterial thylakoid membranes.

The thylakoid membranes of cyanobacteria are the major sites of respiratory electron transport as well as photosynthetic light reactions. The photosynthetic and respiratory electron transport chains share some components, and their presence in the same membrane opens up the possibility for a variety of "unorthodox" electron transport routes. Many of the theoretically possible electron transport pathways have indeed been detected in particular species and circumstances. Electron transport has a crucial impact on the redox balance of the cell and therefore the pathways of electron flow in the cyanobacterial thylakoid membrane must be tightly regulated. This review summarises what is known of cyanobacterial electron transport components, their interactions and their sub-cellular location. The role of thylakoid membrane organisation in controlling electron transport pathways is discussed with respect to recent evidence that the larger-scale distribution of complexes in the membrane is important for controlling electron exchange between the photosynthetic and respiratory complexes. The distribution of complexes on scales of 100nm or more is under physiological control, showing that larger-scale thylakoid membrane re-arrangement is a key factor in controlling the crosstalk between photosynthetic and respiratory electron transport. This article is part of a Special Issue entitled: Dynamic and ultrastructure of bioenergetic membranes and their components.