The biological processes that are the basis of all life forms are mediated largely by protein-protein interactions. The protein complexes involved in these interactions can be categorised by their... Show moreThe biological processes that are the basis of all life forms are mediated largely by protein-protein interactions. The protein complexes involved in these interactions can be categorised by their affinity, which results in a range from static to transient complexes. Electron transfer complexes, which have to combine high turn-over with specificity are typically transient complexes. The transient complexes under investigation in this work are all part of the photosynthetic redox chain, in which electrons are transferred from membrane bound cytochrome f (cytf) to either plastocyanin (Pc) or cytochrome c6 (cytc6). This work describes the investigation of several aspects of transient protein-protein interactions that are applicable to many other transient complexes. The use of NMR as a tool of choice for these studies has proven it an invaluable technique that provides insight in rules that govern the world of transient complex formation. New approaches such as PRE and the creation of ensembles of structures are investigated. They will hopefully lead to a full understanding of dynamics and the variety of ways that transient complexes use dynamics to perform their function in the cell. Show less