Exploring the nature of transient biological electron transfer complexes at the single-molecule level

During photosynthesis and respiration, solar or chemical energy are used to transfer electrons along a chain of proteins to power up a proton battery. Some of these electron transfer (ET) proteins move freely, shuttling electrons back and forth between larger membrane integral proteins. The mystery is how the freely moving proteins find their way to their cognate partner, dock at the membrane surface, release their electron and then undock, all within a few microseconds. Somehow, these pairs of proteins balance conflicting requirements: they must come together quickly and specifically to transfer electrons, yet they must also separate rapidly afterwards to sustain high ET turnover. Therefore, whatever forces brought the proteins together must be subsequently switched into reverse. How is this possible? What is this switch?