Reaction sequences from light absorption to the cleavage of water in photosynthesis.

The reaction sequence between the primary electron acceptor, the oxidized Chlorophyll-a, 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 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-a center with that of S. Beginning with the transfer from the immediate donor, D, to Chl-a, the subsequent transfer from D to D ends in the electron transfer from S to D. 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 O from water takes place. Correlations between the events are described quantitatively. [ABSTRACT FROM AUTHOR]