title: The reactivity of hydrazine with photosystem II strongly depends on the redox state of the water oxidizing system.
abstract: The decay kinetics of the redox states S2 and S3 of the water-oxidizing enzyme have been analyzed in isolated spinach thylakoids in the absence and presence of the exogenous reductant hydrazine. In control samples without NH2NH2 a biphasic decay is observed. The rapid decline of S2 and S3 with YD as reductant exhibits practically the same kinetics with t1/2 = 6-7 s at pH = 7.2 and 7 degrees C. The slow reduction (order of 5-10 min at 7 degrees C) of S2 and S3 with endogenous electron donors other than YD is about twice as fast for S2 as for S3 under these conditions. In contrast, the hydrazine-induced reductive shifts of the formal redox states Si (i = 0...3) are characterized by a totally different kinetic pattern: (a) at 1 mM NH2NH2 and incubation on ice the decay of S2 is estimated to be at least 25 times faster (t1/2 less than or equal to 0.4 min) than the corresponding reaction of S3 (t1/2 approximately 13 min); (b) the NH2NH2-induced decay of S3 is even slower (about twice) than the transformation of S1 into the formal redox state 'S-1' (t1/2 approximately 6 min), which gives rise to the two-digit phase shift of the oxygen-yield pattern induced by a flash train in dark adapted thylakoids. (c) the NH2NH2-induced transformation S0----'S-2' [Renger, Messinger and Hanssum (1990) in: Curr.' Res. Photosynth. (Baltscheffsky, M., ed), Vol. 1, pp. 845-848, Kluwer, Dordrecht] is about three times faster (t1/2 approximately 2 min) than the reaction [see text]. Based on these results, the following dependence on the redox state Si of the reactivity towards NH2NH2 is obtained: S3 less than S1 less than S0 much less than S2. The implications of this surprising order of reactivity are discussed.
authors: Max Volmer Institut für Biophysikalische und Physikalische Chemie, Technischen Universität, Berlin, Germany.
authors: J
authors: J
authors: Messinger
authors: G
authors: G
authors: Renger
mesh_terms: D002736:Chloroplasts / Q000378:metabolism*; D006834:Hydrazines / Q000737:chemistry*; D007700:Kinetics; D008027:Light; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D010944:Plants; D014867:Water / Q000378:metabolism
chemical_list: D006834:Hydrazines; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D014867:Water; C029424:hydrazine; D010100:Oxygen