KINETICS OF S-2 AND S-3 REDUCTION BY TYROSINE-Y-D AND OTHER ENDOGENOUS DONORS AS A FUNCTION OF TEMPERATURE IN SPINACH PS-II MEMBRANE-FRAGMENTS WITH A RECONSTITUTED PLASTOQUINONE POOL

The characteristic period four oscillation patterns of oxygen evolutio n induced by a train of single-turnover flashes were measured as a fun ction of temperature in dark-adapted photosystem II (PS II) membrane f ragments that were reconstituted with native plastoquinone-9 (PQ-9) by a recently developed procedure [Kurreck, J., Seeliger, A. G., Reifart h, F., Karge, M., & Renger, G. (1995) Biochemistry 34, 15721-15731]. T he following results were obtained: (a) within the range 0-35 degrees C, the probabilities of misses (alpha) and double-hits (beta) and the dark population of redox state S-1 exhibit similar dependencies on the temperature; (b) below a characteristic temperature upsilon(c) these parameters remain virtually independent of temperature, above upsilon( c) (upsilon(c) = 20 degrees C for alpha, and beta; upsilon(c) = 30 deg rees C for S-1) the values of alpha and beta increase whereas S-1 decr eases; and (c) the dark decay of S-2 and S-3 via fast and slow kinetic s owing to reduction of the water oxidase by Y-D and other endogenous electron donor(s), respectively, exhibits comparatively strong tempera ture dependencies with the following activation energies: E(A)(S-2(fas t)) = 60 +/- 10 kJ/mol, E(A)(S-3(fast)) = 55 +/- 10 kJ/mol, E(A)(S-2(s low)) = 80 +/- 5 kJ/mol, and E(A)(S-3(slow)) = 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., Schroder, W. P., & Renger, G. (1993) Biochemistry 32, 7658-7668]. The se findings reveal that the reaction coordinates of feeding electrons by endogenous electron donors into the water oxidizing complex (WOC) t hat attains the redox states S-2 and S-3 is virtually invariant to Tri ton X-100 treatment used in the isolation procedure of PS II membrane fragments from thylakoids. Implications of these findings are discusse d.