title: Abnormal S-state turnovers in NH3-binding Mn centers of photosynthetic O2 evolving system.
abstract: The inhibitory effects of NH3 on S-state turnovers were studied by curve fitting and deconvolution of thermoluminescence glow curves and low-temperature EPR spectroscopy. The following results were found: (i) High concentrations of NH3 upshifted the recombination temperatures of both S2QB- and S2QA- charge pairs, indicating formation of an abnormal S2 state having a lowered oxidation potential. (ii) The abnormal S2 was correlated to alterations in EPR multiline signal: high concentrations of NH3 induced the modified multiline signal having reduced hyperfine line spacing, accompanied by disappearance of the g = 4.1 signal, while low concentrations of NH3 reduced the line width of the g = 4.1 signal with a slight shift in its g value to 4.2 concomitant with suppression in amplitude of the normal multiline signal, both suggesting coordination of NH3 to the Mn center. (iii) More than half of the NH3-binding abnormal S2 centers underwent S-state turnover to yield S3QB- and S3QA- pairs having normal thermoluminever, the NH3-binding S3 was unable to undergo further S-state turnovers. (iv) The interruption of S-state turnover at S3 was assumed to be due to the inability of electron abstraction from the S3 state. Based on these, the mechanism of NH3 inhibition was discussed.
authors.affiliation: Solar Energy Research Group, Institute of Physical and Chemical Research, Saitama, Japan.
authors.forename: T A
authors.initials: TA
authors.lastname: Ono
authors.forename: Y
authors.initials: Y
authors.lastname: Inoue
mesh_terms: D000641:Ammonia / Q000378:metabolism* / Q000494:pharmacology; D002734:Chlorophyll / Q000378:metabolism*; D004237:Diuron / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D045342:Light-Harvesting Protein Complexes; D008163:Luminescent Measurements; D008345:Manganese / Q000378:metabolism*; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000187:drug effects; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins; D002734:Chlorophyll; D008345:Manganese; D000641:Ammonia; D004237:Diuron