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COOPERATION OF CHARGES IN PHOTOSYNTHETIC O 2 EVOLUTION–I. A LINEAR FOUR STEP MECHANISM
Author(s) -
KOK BESSEL,
FORBUSH BLISS,
McGLOIN MARION
Publication year - 1970
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1970.tb06017.x
Subject(s) - oxidizing agent , photosynthetic reaction centre , chemistry , trapping , photosynthesis , relaxation (psychology) , ground state , photochemistry , decomposition , chemical physics , atomic physics , physics , electron transfer , psychology , ecology , social psychology , biochemistry , organic chemistry , biology
— Using isolated chloroplasts and techniques as described by Joliot and Joliot[6] we studied the evolution of O 2 in weak light and light flashes to analyze the interactions between light induced O 2 precursors and their decay in darkness. The following observations and conclusions are reported: 1. Light flashes always produce the same number of oxidizing equivalents either as precursor or as O 2 . 2. The number of unstable precursor equivalents present during steady state photosynthesis is ∼ 1.2 per photochemical trapping center. 3. The cooperation of the four photochemically formed oxidizing equivalents occurs essentially in the individual reaction centers and the final O 2 evolution step is a one quantum process. 4. The data are compatible with a linear four step mechanism in which a trapping center, or an associated catalyst, ( S ) successively accumulates four + charges. The S 4+ state produces O 2 and returns to the ground state S 0 . 5. Besides S 0 also the first oxidized state S + is stable in the dark, the two higher states, S 2+ and S 3+ are not. 6. The relaxation times of some of the photooxidation steps were estimated. The fastest reaction, presumably S * 1 ← S 2 , has a (first) half time ≤ 200 μsec. The S * 2 state and probably also the S * 0 state are processed somewhat more slowly (˜ 300–400 μsec).