Electron donors and acceptors in the initial steps of photosynthesis in purple bacteria: a personal account.

The discovery by Louis N. M. Duysens in the 1950s that illumination of photosynthetic purple bacteria can cause oxidation of either a bacteriochlorophyll complex (P) or a cytochrome was followed by an extended period of uncertainty as to which of these processes was the 'primary' photochemical reaction. Similar questions arose later about the roles of bacteriopheophytin (BPh) and quinones as the initial electron acceptor. This is a personal account of kinetic measurements that showed that electron transfer from P to BPh occurs in the initial step, and that the oxidized bacteriochlorophyll complex (P(+)) then oxidizes the cytochrome while the reduced BPh transfers an electron to a quinone.