Photosynthesis in purple bacteria is dependent on light-induced electron transfer in the reaction centre (RC), coupled to the uptake of protons from the cytoplasm. The RC contains a cytochrome molecule which re-reduces the oxidised electron donor.

1: The coupling of light-induced electron transfer and proton uptake as derived from crystal structures of reaction centres from Rhodopseudomonas viridis modified at the binding site of the secondary quinone, QB. Lancaster CR, Michel H; Structure 1997;5:1339-1359. PMID:9351808