Kinetics of S2 and S3 Reduction by Tyrosine YD and Other Endogenous Donors As a Function of Temperature in Spinach PS II Membrane Fragments with a Reconstituted Plastoquinone Pool

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Abstract
The characteristic period four oscillation patterns of oxygen evolution induced by a train of single-turnover flashes were measured as a function of temperature in dark-adapted photosystem II (PS II) membrane fragments that were reconstituted with native plastoquinone-9 (PQ-9) by a recently developed procedure [Kurreck, J., Seeliger, A. G., Reifarth, F., Karge, M., & Renger, G. (1995) Biochemistry 34, 15721−15731]. The following results were obtained: (a) within the range 0−35 °C, the probabilities of misses (α) and double-hits (β) and the dark population of redox state S1 exhibit similar dependencies on the temperature; (b) below a characteristic temperature ϑc these parameters remain virtually independent of temperature, above ϑc (ϑc = 20 °C for α and β; ϑc = 30 °C for S1) the values of α and β increase whereas S1 decreases; and (c) the dark decay of S2 and S3 via fast and slow kinetics owing to reduction of the water oxidase by YD and other endogenous electron donor(s), respectively, exhibits comparatively strong temperature dependencies with the following activation energies: EA(S2fast) = 60 ± 10 kJ/mol, EA(S3fast) = 55 ± 10 kJ/mol, EA(S2slow) = 80 ± 5 kJ/mol, and EA(S3slow) = 75 ± 5 kJ/mol. These values of PQ-9 reconstituted PS II membrane fragments are very similar to those that were previously reported for thylakoids [Messinger, J., Schröder, W. P., & Renger, G. (1993) Biochemistry 32, 7658−7668]. These findings reveal that the reaction coordinates of feeding electrons by endogenous electron donors into the water oxidizing complex (WOC) that attains the redox states S2 and S3 is virtually invariant to Triton X-100 treatment used in the isolation procedure of PS II membrane fragments from thylakoids. Implications of these findings are discussed.