Calcium-specific site influences the structure and activity of the manganese cluster responsible for photosynthetic water oxidation
- Princeton Univ., NJ (USA)
EPR studies have revealed that removal of calcium using citric acid from the site in spinach photosystem II which is coupled to the photosynthetic O{sub 2}-evolving process produces a structural change in the manganese cluster responsible for water oxidation. If done in the dark, this yields a modified S{sub 1}{prime} oxidation state which can be photooxidized above 250 K to form a structurally altered S{sub 2}{prime} state, as seen by formation of a modified multiline EPR signal. Compared to the normal S{sub 2} state, this new S{sub 2}{prime}-state EPR signal has more lines and 25% narrower {sup 55}Mn hyperfine splittings, indicative of disruption of the ligands to manganese. The calcium-depleted S{sub 2}{prime} oxidation state is greatly stabilized compared to the native S{sub 2} oxidation state, as seen by a large increase in the lifetime of the S{sub 2}{prime} EPR signal. Calcium reconstitution results in the reduction of the oxidized tyrosine residue {sup 161}Y{sub D}{sup +} within the reaction center D{sub 1} protein in both the S{sub 1}{prime} and S{sub 2}{prime} states, as monitored by its EPR signal intensity. The authors attribute this to reduction by Mn. Photooxidation of S{sub 2}{prime} above 250 K produces a higher S state having a new EPR signal and a symmetric line width suggestive of oxidation of an organic donor, possibly an amino acid, in magnetic contact with the Mn cluster. This EPR signal forms in a stoichiometry of 1-2 relative to Y{sub D}{sup +}. This state is photoaccumulated, does not evolve O{sub 2}, and decays in the dark to the stable S{sub 2}{prime} state. A gatekeeper role for calcium in limiting access of substrate water to the catalytic Mn cluster is indicated.
- OSTI ID:
- 6920592
- Journal Information:
- Biochemistry; (USA), Vol. 28:24; ISSN 0006-2960
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
MANGANESE COMPLEXES
HYPERFINE STRUCTURE
PHOTOSYNTHETIC REACTION CENTERS
ELECTRON SPIN RESONANCE
WATER
OXIDATION
CALCIUM COMPOUNDS
ELECTRON SPECTRA
LIGANDS
MANGANESE 55
OXYGEN
SPINACH
STOICHIOMETRY
SUBSTRATES
TYROSINE
YTTRIUM ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
AMINO ACIDS
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
COMPLEXES
ELEMENTS
FOOD
HYDROGEN COMPOUNDS
HYDROXY ACIDS
INTERMEDIATE MASS NUCLEI
ISOTOPES
MAGNETIC RESONANCE
MAGNOLIOPHYTA
MAGNOLIOPSIDA
MANGANESE ISOTOPES
NONMETALS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PLANTS
RESONANCE
SPECTRA
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES
VEGETABLES
550601* - Medicine- Unsealed Radionuclides in Diagnostics