title: Effect of bicarbonate on the water-oxidizing complex of photosystem II in the super-reduced S-states.
abstract: It is shown that the hydrazine-induced transition of the water-oxidizing complex (WOC) to super-reduced S-states depends on the presence of bicarbonate in the medium so that after a 20 min treatment of isolated spinach thylakoids with 3 mM NH(2)NH(2) at 20 degrees C in the CO(2)/HCO(3)(-)-depleted buffer the S-state populations are: 42% of S(-3), 42% of S(-2), 16% of S(-1) and even formal S(-4) state is reached, while in the presence of 2 mM NaHCO(3), the same treatment produces 30% of S(-3), 38% of S(-2), and 32% of S(-1) and there is no indication of the S(-4) state. Bicarbonate requirement for the oxygen-evolving activity, very low in untreated thylakoids, considerably increases upon the transition of the WOC to the super-reduced S-states, and the requirement becomes low again when the WOC returns back to the normal S-states using pre-illumination. The results are discussed as a possible indication of ligation of bicarbonate to manganese ions within the WOC.
authors.affiliation: Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow Region 142290, Russia.
authors.forename: Dmitriy N
authors.initials: DN
authors.lastname: Shevela
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Khorobrykh
authors.forename: Vyacheslav V
authors.initials: VV
authors.lastname: Klimov
mesh_terms: D001639:Bicarbonates / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D018724:Spinacia oleracea; D014867:Water / Q000737:chemistry*
chemical_list: D001639:Bicarbonates; D045332:Photosystem II Protein Complex; D014867:Water; D010100:Oxygen