Unique binding site for Mn2+ ion responsible for reducing an oxidized YZ tyrosine in manganese-depleted photosystem II membranes.
Binding of Mn2+ to manganese-depleted photosystem II and electron donation from the bound Mn2+ to an oxidized YZ tyrosine were studied under the same equilibrium conditions. Mn2+ associated with the depleted membranes in a nonsaturating manner when added alone, but only one Mn2+ ion per photosystem II (PS II) was bound to the membranes in the presence of other divalent cations including Ca2+ and Mg2+. Mn2+-dependent electron donation to photosystem II studied by monitoring the decay kinetics of chlorophyll fluorescence and the electron paramagnetic resonance (EPR) signal of an oxidized YZ tyrosine (YZ+) after a single-turnover flash indicated that the binding of only one Mn2+ ion to the manganese-depleted PS II is sufficient for the complete reduction of YZ+ induced by flash excitation. The results indicate that the manganese-depleted membranes have only one unique binding site, which has higher affinity and higher specificity for Mn2+ compared with Mg2+ and Ca2+, and that Mn2+ bound to this unique site can deliver an electron to YZ+ with high efficiency. The dissociation constant for Mn2+ of this site largely depended on pH, suggesting that a single amino acid residue with a pKa value around neutral pH is implicated in the binding of Mn2+. The results are discussed in relation to the photoactivation mechanism that forms the active manganese cluster.
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Laboratory for Photo-Biology, RIKEN Photodynamics Research Center, The Institute of Physical and Chemical Research, Sendai, Japan. takaaki@postman.riken.go.jp
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D001665:Binding Sites; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D000077194:Chlorophyll A; D002736:Chloroplasts / Q000737:chemistry / Q000378:metabolism; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D008345:Manganese / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D010782:Photolysis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D013050:Spectrometry, Fluorescence; D018724:Spinacia oleracea; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism
D005609:Free Radicals; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C114979:tyrosyl radical YZ; D002734:Chlorophyll; D014443:Tyrosine; D008345:Manganese; D000077194:Chlorophyll A