Functional differences of photosystem II from Synechococcus elongatus and spinach characterized by flash induced oxygen evolution patterns

• Detailed comparative studies of flash induced oxygen evolution patterns in thylakoids from the thermophilic cyanobacterium Synechococcus elongatus (S. elongatus; also referred to as Thermosynechococcus elongatus) and from spinach led to the following results: (i) the miss parameter cc of S. elongatus thylakoids exhibits a pronounced temperature dependence with a minimum of 7% at 25 degreesC and values of 17 and 10% at 3 and 35 degreesC, respectively, while for spinach thylakoids alpha decreases continuously from 18% at 35 degreesC down to 8% at 3 degreesC; (ii) at all temperatures, the double hit probability exceeds in S. elongatus the corresponding values of spinach by an increment Deltabeta of about 3%; (iii) at 20 degreesC the slow relaxation of the oxidation states S-2 and S-3 is about 15 and 30 times, respectively, slower in S. elongatus than in spinach, while the reduction of these S states by tyrosine Y-D is 2-3 times faster; (iv) the reaction SOYDox --> S1YD is slower by a factor of 4 in S. elongatus as compared to spinach; and (v) the activation energies of S state dark relaxations in S. elongatus are all within a factor of 1.5 as compared to the previously reported values from spinach thylakoids [Vass, I., Deak, Z., and Hideg, E. (1990) Biochim. Biophys. Acta 1017, 63-69; Messinger, J., Schroder, W. P., and Renger, G. (1993) Biochemistry 32, 7658-7668], but the difference between the activation energies of the Slow S-2 and S-3 decays is significantly larger in S. elongatus than in spinach. These results are discussed in terms of differences between cyanobacteria and higher plants on the acceptor side of PSII and a shift of the redox potential of the couple Y-D/Y-D(ox). The obtained data are also suitable to address questions about effects of the redox state of Y-D on the miss probability and the possibility of an S state dependent miss parameter.

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NATURVETENSKAP  -- Biologi -- Biokemi och molekylärbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Biochemistry and Molecular Biology (hsv//eng)

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