Light-induced proton release and proton uptake reactions in the cyanobacterrial phytochrome Cph1

The transition of Synechocystis PCC 6803 phytochrome Cph1 and its N-terrminal sensor domain from Pr to Pfr leads to net proton release, which is a function of proton release from decay of an intermediate and of proton uptake associated with Pfr formation. Protons arise from ionizable amino acid side chains.