P680

A special form of *chlorophyll a with a light absorption peak of 684 nm. It is one of the constituents of the *photosystem II light-gathering centre of photosynthesis. The absorption of light energy by the P680 molecules causes, among other things, the formation of a strong oxidant that can then oxidize water. This results in the evolution of molecular oxygen and initiates electron flow, which continues, via *photosystem I, through to the production of reduced *NADP. See also P700.