Ammonia binds to the catalytic manganese of the oxygen-evolving complex of photosystem II. Evidence by electron spin-echo envelope modulation spectroscopy
Ammonia binds to the catalytic manganese of the oxygen-evolving complex of photosystem II. Evidence by electron spin-echo envelope modulation spectroscopy
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氨与光系统 II 的放氧复合物的催化锰结合。
DOI：
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发表时间：
1989
期刊：
影响因子：
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通讯作者：
M. Klein
中科院分区：
文献类型：
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作者：
R. Britt;J. Zimmermann;K. Sauer;M. Klein
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.
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.