Kulandaivelu G, Senger H
Biochim Biophys Acta. 1976 Apr 9;430(1):94-104. doi: 10.1016/0005-2728(76)90225-5.
The kinetics (region of seconds) of the light-induced 520 nm absorbance changes and its dark reversal have been studied in detail in the wild type and in some pigment and photosynthetic mutants of Scenedesmus obliquus. The following 5 lines of evidence led us to conclude that the signal is entirely due to the photosystem I reaction modified by electron flow from Photosystem II. Gradual blocking of the electron transport with 3(3,4-dichlorophenyl)-1,1-dimethylurea resulted in diminution and ultimate elimination of the biphasic nature of the signal without reducing the extent of the absorbance change or of the dark kinetics. On the contrary, blocking electron flow at the oxidizing side of plastoquinone with 2,5-dibromo-3-methyl-6-isoprophyl-p-benzoquinone or inactivating the plastocyanin with KCN, prolonged the dark reversal of the absorbance change apart from abolishing the biphasic nature of the signal. Action spectra clearly indicate that the main signal (I) is due to electron flow in Photosystem I and that its modification (Signal II) is due to the action of Photosystem II. Signal I is pH independent, whereas Signal II demonstrates a strong pH dependence, parallel to the O2-evolving capacity of the cells. Chloroplast particles isolated from the wild type Scenedesmus cells demonstrated in the absence of any added artificial electron donor or acceptor and also under non-phosphorylation conditions the 520 nm absorbance change with approximately the same magnitude as whole cells. The dark kinetics of the particles were comparatively slower. Removal of plastocyanin and other electron carriers by washing with Triton X-100 slowed down the kinetics of the dark reversal reaction to a greater extent. A similar positive absorbance change at 520 nm and slow dark reversal was also observed in the Photosystem I particles prepared by the Triton method. Mutant C-6E, which contains neither carotenoids nor chlorophyll b and lacks Photosystem II activity, demonstrates a normal signal I of the 520 nm absorbance change. This latter result contradicts the postulate that carotenoids are the possible cause of the 520 nm absorbance change.
在斜生栅藻的野生型以及一些色素和光合突变体中，已对光诱导的520nm吸光度变化的动力学（秒级范围）及其暗逆转进行了详细研究。以下五条证据使我们得出结论，该信号完全归因于由光系统II的电子流修饰的光系统I反应。用3-(3,4-二氯苯基)-1,1-二甲基脲逐渐阻断电子传递，导致信号的双相性质减弱并最终消除，而不会降低吸光度变化的程度或暗动力学。相反，用2,5-二溴-3-甲基-6-异丙基对苯醌在质体醌的氧化侧阻断电子流或用KCN使质体蓝素失活，除了消除信号的双相性质外，还延长了吸光度变化的暗逆转。作用光谱清楚地表明，主要信号（I）归因于光系统I中的电子流，其修饰（信号II）归因于光系统II的作用。信号I与pH无关，而信号II表现出强烈的pH依赖性，与细胞的放氧能力平行。从野生型斜生栅藻细胞中分离出的叶绿体颗粒，在没有添加任何人工电子供体或受体的情况下，以及在非磷酸化条件下，也表现出与完整细胞大致相同幅度的520nm吸光度变化。颗粒的暗动力学相对较慢。用Triton X-100洗涤去除质体蓝素和其他电子载体，在更大程度上减慢了暗逆转反应动力学。在用Triton方法制备的光系统I颗粒中，也观察到了类似的520nm正吸光度变化和缓慢的暗逆转。突变体C-6E既不含类胡萝卜素也不含叶绿素b，并且缺乏光系统II活性，表现出正常的520nm吸光度变化信号I。后一结果与类胡萝卜素是520nm吸光度变化可能原因的假设相矛盾。
