Structural organization of proteins on the oxidizing side of photosystem II. Two molecules of the 33-kDa manganese-stabilizing proteins per reaction center.
The 33-kDa manganese-stabilizing protein stabilizes the manganese cluster in the oxygen-evolving complex. There has been, however, a considerable amount of controversy concerning the stoichiometry of this photosystem II (PS II) component. In this paper, we have verified the extinction coefficient of the manganese-stabilizing protein by amino acid analysis, determined the manganese content of oxygen-evolving photosystem II membranes and reaction center complex using inductively coupled plasma spectrometry, and determined immunologically the amount of the manganese-stabilizing protein associated with photosystem II. Oxygen-evolving photosystem II membranes and reaction center complex preparations contained 258 +/- 11 and 67 +/- 3 chlorophyll, respectively, per tetranuclear manganese cluster. Immunoquantification of the manganese-stabilizing protein using mouse polyclonal antibodies on "Western blots" demonstrated the presence of 2.1 +/- 0.2 and 2.0 +/- 0.3 molecules of the manganese-stabilizing protein/tetranuclear manganese cluster in oxygen-evolving PS II membranes and highly purified PS II reaction center complex, respectively. Since the manganese-stabilizing protein co-migrated with the D2 protein in our electrophoretic system, accurate immunoquantification required the inclusion of CaCl2-washed PS II membrane proteins or reaction center complex proteins in the manganese-stabilizing protein standards to compensate for the possible masking effect of the D2 protein on the binding of the manganese-stabilizing protein to Immobilon-P membranes. Failure to include these additional protein components in the manganese-stabilizing protein standards leads to a marked underestimation of the amount of the manganese-stabilizing protein associated with these photosystem II preparations.
Xu
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Department of Botany, Louisiana State University, Baton Rouge 70803-1705.
Bricker
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D002736:Chloroplasts / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D008345:Manganese / Q000302:isolation & purification / Q000378:metabolism*; D008970:Molecular Weight; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000302:isolation & purification / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000302:isolation & purification / Q000378:metabolism*; D010944:Plants / Q000378:metabolism*; D011506:Proteins
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D011506:Proteins; C054266:photosystem II manganese-stabilizing protein; D008345:Manganese; D010100:Oxygen