Calcium depletion from the photosynthetic water-oxidizing complex reveals photooxidation of a protein residue

Abstract

A new intermediate in the water-oxidizing reaction has been observed in spinach photosystem II (PSII) membranes that are depleted of Ca2+ from the site which is conformationally coupled to the manganese cluster comprising the water-oxidizing complex (WOC). It gives rise to a recently identified EPR signal (symmetric line shape with width 163 +/- 5 G, g = 2.004 +/- 0.005), which forms in samples inhibited either by depletion of Ca2+ [Boussac, A., Zimmerman, J.-L., & 28, 8984-8989; Sivaraja, M., Tso, J., & Dismukes, G.C. (1989) Biochemistry 28 9459-9464] or by substitution of Cl- by F- (Baumgarten, Philo, and Dismukes, submitted for publication). Further characterization of this EPR signal has revealed the following: (1) it forms independently of the local structure of the PSII acceptors; (2) it arises from photooxidation of a PSII species that donates an electron to Tyr-Z+ or to the Mn cluster in competition with an exogenous donor (DPC); (3) the Curie temperature dependence of the intensity suggests an isolated doublet ground state, attributable to a spin S = 1/2 radical; (4) the electron spin orientation relaxes 1000-fold more rapidly than typical for a free radical, exhibiting a strong temperature dependence of P1/2 (half-saturation power approximately T3.4) and a broad inhomogeneous line width; (5) it yields an undetectable change in the magnetic susceptibility upon formation by a laser flash; (6) it disappears in parallel with release of Mn during reduction with NH2OH, indicating that it forms only in the presence of the modified Mn cluster. (ABSTRACT TRUNCATED AT 250 WORDS)

Flash induced XANES spectroscopy for the Ca‐depleted Mn‐cluster in the photosynthetic O2‐evolving enzyme

“…After three flashes, the K-edge energy was again up-shifted by 0.2 eV to reach around 70% of a steady-state level found after continuous illumination where the K-edge energy was higher by 0.9 eV than that after one flash. Since illumination of the Ca-depleted S-state gives rise to the formation of a g = 2 EPR signal [7,9,, we may conclude that the up-shift in Mn K-edge parallels the formation of the g = 2 EPR state. This view is furthermore supported by the fact that the flash pattern of the Kedge energy change subsequent to the first flash is quite similar to the reported flash pattern for the formation of the g = 2 EPR signal [9,14].…”

“…Illuminating the low-pH treated PSI1 membranes results in formation of a modified S-state as indicated by an altered multiline EPR signal , and an upshifted thermoluminescence band [8,11,12]. Further illumination of the abnormal S-state with a single flash or continuous illumination induces an EPR signal in the g = 2 region [7,9]. A quite similar EPR signal was also reported in the PSI1 membranes that were depleted of Ca by treatment with high concentrations of NaCl [13-161, and …”

Investigation of the origin of the "S3" EPR signal from the oxygen-evolving complex of photosystem 2: the role of tyrosine Z

“…The citrate-washed preparation was reported to be isolated in an S/ state, requiring the removal of a single electron to generate the modified S2 state. Addition of calcium to citrate-washed samples in the dark resulted in the reduction in size of the YD+ EPR signal (Sivaraja et al, 1989;Tso et al, 1991b), an effect not observed with pH 6.5 NaCl-washed samples (Boussac et al, 1989;Lockett et al, 1990) but also observed by Lockett et al (1990) in pH 8.3 NaCl-washed samples.…”

The role of Ca2+ ions in modulating changes induced in bean plants by an excess of Cu2+ ions. Chlorophyll fluorescence measurements

“…Therefore, it was postulated that Cu 2+ can act also on PSII activity through interference with Ca 2+ ions. Calcium akppears to be indispensable for normal functioning of the photosynthetic akpparatus, especially at the lumen side of PSII ( Ghanotakis and Yocum 1990; Tso et al 1991; Burda et al 1995; Ramalho et al 1995), CF 0 CF 1 ( Chiang and Dilley 1989; Ramalho et al 1995) and the Calvin cycle ( Kreimer et al 1988). Excess Cu 2+ in in vitro conditions can substitute for Ca 2+ in the OEC ( Hoganson et al 1991; Šeršeň et al 1997) and in CF 0 CF 1 ( Uribe and Stark 1982), leading to a decrease of phosphorylation processes and PSII activity connected with increase of energy loss in the form of heat ( Krieger and Weis 1993).…”