Ammonia binds to the catalytic Mn of the oxygen-evolving complex of photosystem II: Evidence by electron spin-echo envelope modulation spectroscopy
- Lawrence Berkeley Lab., CA (USA)
The mechanism of ammonia inhibition of photosynthetic oxygen evolution has been examined by the pulsed EPR technique of electron spin-echo envelop modulation (ESEEM), revealing the direct coordination of an ammonia-derived ligand to the catalytic Mn complex during the S{sub 1} {yields}S{sub 2} transition of the oxygen evolution S-state cycle. ESEEM experiments were performed on the multiline Mn EPR signal observed in photosystem II enriched spinach thylakoid membranes which were treated with either {sup 14}NH{sub 4}Cl or {sup 15}NH{sub 4}Cl (100 mM, pH 7.5). {sup 15}NH{sub 4}Cl treatment produced modulation of the electron spin-echo signal which arises from an I = 1/2 {sup 15}N nucleus with an isotropic hyperfine coupling A({sup 15}N) = 3.22 MHz. {sup 14}NH{sub 4}Cl treatment produced a different ESEEM pattern resulting from an I = 1 {sup 14}N nucleus with A({sup 14}N) = 2.29 MHz, and with electric quadrupole parameters e{sup 2}qQ = 1.61 MHz and {eta} = 0.59. The {sup 14}n electric quadrupole parameters are interpreted with respect to possible chemical structures for the ligand. An amido (NH{sub 2}) bridge between metal ions is proposed as the molecular identity of the ammonia-derived ligand to the catalytic Mn of photosystem II.
- OSTI ID:
- 6836074
- Journal Information:
- Journal of the American Chemical Society; (USA), Vol. 111:10; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
PHOTOSYNTHESIS
MECHANICS
AMMONIA
DATA ANALYSIS
ELECTRON SPECTROSCOPY
EXPERIMENTAL DATA
MANGANESE
MEASURING INSTRUMENTS
MEASURING METHODS
CHEMICAL REACTIONS
DATA
ELEMENTS
HYDRIDES
HYDROGEN COMPOUNDS
INFORMATION
METALS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NUMERICAL DATA
PHOTOCHEMICAL REACTIONS
SPECTROSCOPY
SYNTHESIS
TRANSITION ELEMENTS
400000* - Chemistry
400200 - Inorganic
Organic
& Physical Chemistry