Ammonia binds to the catalytic manganese of the oxygen-evolving complex of photosystem II. Evidence by electron spin-echo envelope modulation spectroscopy

摘要: The mechanism of ammonia inhibition photosynthetic oxygen evolution has been examined by the pulsed EPR technique electron spin-echo envelop modulation (ESEEM), revealing direct coordination an ammonia-derived ligand to catalytic Mn complex during S{sub 1} {yields}S{sub 2} transition S-state cycle. ESEEM experiments were performed on multiline signal observed in photosystem II enriched spinach thylakoid membranes which treated with either {sup 14}NH{sub 4}Cl or 15}NH{sub (100 mM, pH 7.5). treatment produced arises from I = 1/2 15}N nucleus isotropic hyperfine coupling A({sup 15}N) 3.22 MHz. a different pattern resulting 1 14}N 14}N) 2.29 MHz, and electric quadrupole parameters e{sup 2}qQ 1.61 MHz {eta} 0.59. 14}n are interpreted respect possible chemical structures for ligand. An amido (NH{sub 2}) bridge between metal ions is proposed as molecular identity II.