Analyses of pH-induced modifications of the period four oscillation of flash-induced oxygen evolution reveal distinct structural changes of the photosystem II donor side at characteristic pH values.
This study presents a thorough analysis of the reaction pattern of flash-induced oxygen evolution in spinach thylakoids as a function of pH (4.5 < or = pH < or = 9) and the redox state of tyrosine YD in polypeptide D2. Evaluation of the experimental data within the conventional Kok model [Kok, B., Forbush, B., & McGloin, M. (1970) Photochem. Photobiol. 11, 457-475] led to the following results: (1) the probability of the miss factor is strongly pH dependent (with a pronounced minimum near neutral pH) while the double hit factor is less affected; (2) a marked increase of the apparent S0 population arises at alkaline pH in dark-adapted samples where most of the YD is reduced, but this effect is absent if the percentage of PS II containing the oxidized form YDox is high; and (3) the lifetimes of S2 and S3 exhibit a characteristic pH dependence that is indicative of conformational changes of functional relevance within the water-oxidizing complex and its environment; (4) the kinetic interaction of redox states S2 and S3 with YD is characterized by a change of its behavior at a threshold pH of 6.5-7.0; and (5) at acidic pH values the extent of S2 and S3 reduction by YD decreases concomitant with the occurrence of a very fast decay kinetics. On the basis of a detailed discussion of these results and data from the literature, the water oxidase is inferred to undergo structural changes at pH values of 5-5.5 and 6.5-7.0. These transitions are almost independent of the redox state Si and modify the reaction coordinates of the water oxidase toward endogenous reductants.
Messinger
J
J
Max-Volmer-Institut für Biophysikalische und Physikalische Chemie, Technische Universität Berlin, FRG.
Renger
G
G
D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D011487:Protein Conformation
D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010100:Oxygen