Hulsebosch R J, Hoff A J, Shuvalov V A
Department of Biophysics, Huygens Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands.
Institute of Chem. Phys. Biology, Moscow State University, Vorob'evi Hills, 119899 Moscow, Russia.
Biochim Biophys Acta. 1996 Nov 12;1277(1-2):103-106.
An EPR signal at g = 6.8 attributed to the cytochrome (Cyt) b-559 heme Fe(III) ligated by OH (Fiege, R., Schrieber, U., Lubitz, W., Renger, G. and Shuvalov, V.A. (1995) FEBS Lett. 377, 325-329) was studied. This signal is observed in intact chloroplasts when oxidized by 10 mM 2,3-dicyano,5,6-dichloro-p-benzoquinone (DDQ), but not when 5 mM p-benzoquinone is added. Addition of KF (100 mM) or removal of Ca 21 for blocking the water-oxidizing complex considerably decreases the heme Fe(III)-OH EPR signal. In contrast, DCMU does not decrease this signal and does not influence its photochemical changes at 140 K. Thus, the EPR spectrum of Cyt b-559 Fe(III) ligated by OH is not affected by changes at the acceptor side of Photosystem 11, and its photochemical decrease is probably not due to reduction via the acceptor side. Comparison of the effect of KF on the model heme Fe(III) in myoglobin (Mb) at pH 10.5 shows that F replaces OH as a ligand at the sixth coordination position of the heme Fe(III) in both Mb and chloroplasts Cyt b-559. This replacement is accompanied by changes of the symmetry of the molecular field causing a disappearance of the EPR signals at g = 6.8 and 5.0. Our results provide further evidence for a possible participation of the Cyt b-559 heme Fe ligated by OH in photosynthetic water oxidation.
研究了一种g = 6.8的电子顺磁共振（EPR）信号，该信号归因于被OH连接的细胞色素（Cyt）b - 559血红素Fe(III)（菲格，R.，施里伯，U.，卢比茨，W.，伦格，G.和舒瓦洛夫，V.A.（1995年）《欧洲生物化学学会联合会快报》377卷，325 - 329页）。当完整的叶绿体被10 mM 2,3 - 二氰基 - 5,6 - 二氯 - 对苯醌（DDQ）氧化时可观察到该信号，但添加5 mM对苯醌时则观察不到。添加氟化钾（100 mM）或去除钙离子以阻断水氧化复合物，会显著降低血红素Fe(III) - OH的EPR信号。相比之下，二氯苯基二甲基脲（DCMU）不会降低该信号，也不会影响其在140 K时的光化学变化。因此，被OH连接的Cyt b - 559 Fe(III)的EPR谱不受光系统II受体侧变化的影响，其光化学降低可能不是由于通过受体侧的还原作用。在pH 10.5时，氟化钾对肌红蛋白（Mb）中模型血红素Fe(III)的影响比较表明，在Mb和叶绿体Cyt b - 559中，F取代OH作为血红素Fe(III)第六配位位置的配体。这种取代伴随着分子场对称性的变化，导致g = 6.8和5.0处的EPR信号消失。我们的结果为被OH连接的Cyt b - 559血红素Fe可能参与光合水氧化提供了进一步的证据。
