Van Gorkom H J, Pulles M P, Wessels J S
Biochim Biophys Acta. 1975 Dec 11;408(3):331-9. doi: 10.1016/0005-2728(75)90134-6.
Photosystem II reaction center components have been studied in small system II particles prepared with digitonin. Upon illumination the reduction of the primary acceptor was indicated by absorbance changes due to the reduction of a plastoquinone to the semiquinone anion and by a small blue shifts of absorption bands near 545 nm (C550) and 685 nm. The semiquinone to chlorophyll ratio was between 1/20 and 1/70 in various preparations. The terminal electron donor in this reaction did not cause large absorbance changes but its oxidized form was revealed by a hitherto unknown electron spin resonance (ESR) signal, which had some properties of the well-known signal II but a linewidth and g-value much nearer to those of signal I. Upon darkening absorbance and ESR changes decayed together in a cyclic or back reaction which was stimulated by 3-(3,4 dichlorophenyl)-1,1-dimethylurea. The donor could be oxidized by ferricyanide in the dark. Illumination in the presence of ferricyanide induced absorbance and ESR changes, rapidly reversed upon darkening, which may be ascribed to the oxidation of a chlorophyll a dimer, possibly the primary electron donor of photosystem II. In addition an ESR signal with 15 to 20 gauss linewidth and a slower dark decay was observed, which may have been caused by a secondary donor.
利用洋地黄皂苷制备的小型光系统II颗粒对光系统II反应中心成分进行了研究。光照时，初级受体的还原可通过以下现象表明：因质体醌还原为半醌阴离子导致的吸光度变化，以及545nm（C550）和685nm附近吸收带的小幅蓝移。在各种制剂中，半醌与叶绿素的比例在1/20至1/70之间。该反应中的末端电子供体不会引起大的吸光度变化，但其氧化形式可通过一种迄今未知的电子自旋共振（ESR）信号显示出来，该信号具有一些著名的信号II的特性，但线宽和g值更接近信号I。暗化时，吸光度和ESR变化在由3 -（3,4 -二氯苯基）-1,1 -二甲基脲刺激的循环或逆向反应中一起衰减。供体在黑暗中可被铁氰化物氧化。在铁氰化物存在下光照会引起吸光度和ESR变化，暗化时迅速逆转，这可能归因于叶绿素a二聚体的氧化，可能是光系统II的初级电子供体。此外，还观察到一种线宽为15至20高斯且暗衰减较慢的ESR信号，这可能是由次级供体引起的。
