Reaction Sequences from Light Absorption to the Cleavage of Water in Photosynthesis—Routes, Rates and Intermediates

Abstract

AbstractThe reaction sequence between the primary electron acceptor, the oxidized Chlorophyll‐aII, and the terminal electron donor, the water splitting enzyme system S, is being described in the range from nanoseconds to milliseconds. For the cleavage of water Chlorophyll‐a+II extracts four electrons in four turnovers from the enzyme system S responsible for the water oxidation. For each extraction the electron is moved step by step along the chain that connects the Chlorophyll‐aII center with that of S. Beginning with the transfer from the immediate donor, D1 to Chl‐a+II, the subsequent transfer from D2 to D+I ends in the electron transfer from S to D2+. This final act establishes in S the oxidizing equivalent, probably in the form of oxidized manganese. Coupled with these acts is an intrinsic proton release and a surplus charge formation. After the generation of the 4th oxidizing equivalent in a concerted final action the evolution of O2 from water takes place. Correlations between the events are described quantitatively.