COOPERATION OF CHARGES IN PHOTOSYNTHETIC O₂ EVOLUTION–I. A LINEAR FOUR STEP MECHANISM

Abstract

Abstract— Using isolated chloroplasts and techniques as described by Joliot and Joliot[6] we studied the evolution of O2 in weak light and light flashes to analyze the interactions between light induced O2 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 O2. 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 O2 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 S4+ state produces O2 and returns to the ground state S0. 5. Besides S0 also the first oxidized state S+ is stable in the dark, the two higher states, S2+ and S3+ are not. 6. The relaxation times of some of the photooxidation steps were estimated. The fastest reaction, presumably S*1←S2, 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).

Response of isolated thylakoid membranes with altered fluidity to short term heat stress

“…Decomposition of the oxygen burst decay was performed by fitting the curve with a function with two exponential components. The initial S 0 state distribution in dark, misses (α) and double hits (β) were calculated by a software based on fitting of the experimentally obtained oxygen flash yields to the theoretically calculated yields according to the model of Kok et al (1970).…”

Mechanistic Parameters of Electrocatalytic Water Oxidation on LiMn2O4 in Comparison to Natural Photosynthesis

“…The structure of the active site is known with high resolution8, 9, 19 and furthermore, the active states have been studied for decades by various experimental and theoretical methods 2, 10, 11, 12, 20, 21, 22, 23. The mechanism of water oxidation in natural photosynthesis is the so‐called S‐state cycle or Kok cycle24 (Figure 1). In the dark‐stable state S 1 , the four Mn ions have an average valence of Mn 3.5+ .…”

Energy conservation in the photochemical reactions of photosynthesis and its relation to delayed fluorescence

“…equate this rate with Lavorel's J, so that The dependence of delayed fluorescence on the redox state of the donor pool has been shown by observing the emission elicited by flashes of light [71] . The intensity showed a periodicity which was similar to that of oxygen yield [72,73] except that the maxima were displaced. Barbieri et al [71] interpret their experiments as indicating a dependence of emission intensity on the redox state of the oxygen evolving mechanisms [72,73] .…”

“…The intensity showed a periodicity which was similar to that of oxygen yield [72,73] except that the maxima were displaced. Barbieri et al [71] interpret their experiments as indicating a dependence of emission intensity on the redox state of the oxygen evolving mechanisms [72,73] . Chemiluminescence experiments suggest that similar light emission in bacterial chromatophores can result from the return of electrons to oxidized reaction centre chlorophyll from physiological electron acceptors [74].…”