title: Correlation of reaction-center chlorophyll (P-700) oxidation and bound iron-sulfur protein photoreduction in chloroplast photosystem I at low temperatures.
abstract: The extent of P-700 photooxidation at 18 degrees K has been followed in three different chloroplast preparations (unfractionated chloroplasts and two preparations enriched in Photosystem I). More than 90% of P-700+ formation in all preparations was eliminated by the addition of sodium dithionite at pH 10. Photoreduction of a bound chloroplast iron-sulfur protein was also decreased by at least 90% under similar conditions. Electron paramagnetic resonance spectra of the chloroplast preparations in the presence of dithionite showed chemical reduction of bound iron-sulfur protein under conditions where primary photochemistry is eliminated. These results indicate that P-700 photooxidation is concomitant with photoreduction of a bound iron-sulfur protein and that this iron-sulfur protein functions as the primary electron acceptor of Photosystem I.
mesh_terms: D001665:Binding Sites; D002734:Chlorophyll / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism*; D003624:Darkness; D004227:Dithionite; D005615:Freezing; D007700:Kinetics; D008027:Light; D008667:Metalloproteins / Q000378:metabolism*; D010084:Oxidation-Reduction; D010777:Photochemistry; D010788:Photosynthesis; D010944:Plants; D011485:Protein Binding
chemical_list: D003580:Cytochromes; D008667:Metalloproteins; D002734:Chlorophyll; D004227:Dithionite