Under photoinhibitory illumination of spinach PSII membranes, the oxygen-evolving complex subunits, OEC33, 24 and 18, were released from PSII. The liberated OEC33 and also OEC24 to a lesser extent were subsequently damaged and then exhibited smeared bands in SDS/urea-PAGE. Once deteriorated, OEC33 could not bind to PSII. The effects of scavengers and chelating reagents on the damage indicated t...

Aberrant nuclear factor-erythroid 2 (NRF2) expression correlates with tumor development. We investigated NRF2 expression in ovarian epithelial carcinoma (OEC), aiming to identify associations with clinicopathological factors, hormones and induced reactive oxygen species (ROS). Immunohistochemical staining for NRF2 expression was performed on 10 be...

Photosynthesis of green plants, algae and cyanobacteria is powered by sunlight. It uses water as ultimate donor of electrons for the reduction of CO2 to yield carbohydrates. Photosystem II (PS II), a water^ plastoquinone oxidoreductase, is the key enzyme of oxygenic photosynthesis. It is an integral protein of the thylakoid membrane. PS II is functionally bipartite, its photosynthetic reaction ...

Metal–oxygen adducts (Mx Ox, x=1 or 2), such as metal– superoxo, –peroxo, and –oxo species, are key intermediates often detected in the catalytic cycles of dioxygen activation by metalloenzymes. In biomimetic and synthetic chemistry, numerous Mx Ox complexes have been prepared and characterized with various physicochemical methods as structural and functional models of enzymes. Among the Mx O2 ...

The recent finding of a transition state with a significantly lower barrier than previously found, has made the mechanism for O-O bond formation in photosystem II much clearer. The full mechanism can be described in the following way. Electrons and protons are ejected from the oxygen-evolving complex (OEC) in an alternating fashion, avoiding unnecessary build-up of charge. The S0-S1 and S1-S2 t...

We propose a model for the water-oxidation and recovery systems of the oxygen-evolving complex (OEC) of the photosystem II (PSII) enzyme. The whole system is constructed from two catalytic cycles, conducted as a tandem reaction: (i) a water-oxidation loop uses cerium(IV) ammonium nitrate as an oxidant to activate a dimanganese complex for water-oxidation and thereby liberate a molecule of O2 an...

Manganese redox enzymes play crucial roles in a variety of biological systems. These include the photosynthetic oxidation of water m dioxygen, the disproport ionat ion of hydrogen peroxide, the disproport ionat ion of superoxide, and ribonucleotide reduction. The Mn sites in two of these systems, the photosynthetic oxygen evolving complex (OEC) and the Mn catalase from L. planrarum have been ch...

Water oxidation, forming O(2) from water and sunlight, is a fundamental process for life on earth. In nature, the enzyme photosystem II (PSII) catalyzes this reaction. The oxygen evolving complex (OEC), the complex within PSII that catalyzes the actual formation of the O-O bond, contains four manganese atoms and one calcium atom connected by oxo bonds. Seven amino acid side chains in the struct...

The study was carried out on healthy Friesian calves (n = 10) aged between 10 and 30 days. Hypochloremia and alkalosis were induced by intravenous administration of furosemide and isotonic sodium bicarbonate. The venous and arterial blood samples were collected repeatedly. 2,3-diphosphoglycerate (2,3-DPG), hemoglobin and plasmatic chloride concentrations were determined. The red blood cell chlo...

Photosystem II (PSII), which catalyzes photosynthetic water oxidation, is composed of more than 20 subunits, including membrane-intrinsic and -extrinsic proteins. The PSII extrinsic proteins shield the catalytic Mn4CaO5 cluster from the outside bulk solution and enhance binding of inorganic cofactors, such as Ca(2+) and Cl(-), in the oxygen-evolving center (OEC) of PSII. Among PSII extrinsic pr...