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首页> 外文期刊>Biochemistry >Two Redox-Active beta-Carotene Molecules in Photosystem II.
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Two Redox-Active beta-Carotene Molecules in Photosystem II.

机译：两种氧化还原活性β-胡萝卜素分子在照相系统II中。

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摘要

Photosystem II (PS II) contains secondary electron-transfer paths involving cytochrome b(559) (Cyt b(559)), chlorophyll (Chl), and beta-carotene (Car) that are active under conditions when oxygen evolution is blocked such as in inhibited samples or at low temperature. Intermediates of the secondary electron-transfer pathways of PS II core complexes from Synechocystis PCC 6803 and Synechococcus sp. and spinach PS II membranes have been investigated using low temperature near-IR spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. We present evidence that two spectroscopically distinct redox-active carotenoids are formed upon low-temperature illumination. The Car(+) near-IR absorption peak varies in wavelength and width as a function of illumination temperature. Also, the rate of decay during dark incubation of the Car(+) peak varies as a function of wavelength. Factor analysis indicates that there are two spectral forms of Car(+) (Car(A)(+) has an absorbance maximum of 982 nm, and Car(B)(+) has an absorbance maximum of 1027 nm) that decay at different rates. In Synechocystis PS II, we observe a shift of the Car(+) peak to shorter wavelength when oxidized tyrosine D (Y(D)(*)) is present in the sample that is explained by an electrostatic interaction between Y(D)(*) and a nearby beta-carotene that disfavors oxidation of Car(B). The sequence of electron-transfer reactions in the secondary electron-transfer pathways of PS II is discussed in terms of a hole-hopping mechanism to attain the equilibrated state of the charge separation at low temperatures.
机译：光照II（PS II）含有涉及细胞色素B（559）（559）的二次电子转移路径（CYT B（559）），叶绿素（CHL）和β-胡萝卜素（轿车），当氧气进化被阻断时是有效的，例如在抑制样品或低温下。来自SyneChocystis PCC 6803和SyneChococcus SP的PS II核心复合物二次电子转移途径的中间体。使用低温接近IR光谱和电子顺磁共振（EPR）光谱研究已经研究了菠菜PS II膜。我们介绍了在低温照明时形成两个光谱上不同的氧化还原活性类胡萝卜素。汽车（+）接近IR吸收峰值随着照明温度的函数而变化波长和宽度。而且，诸如汽车（+）峰值的暗孵育期间的衰减速率随波长的函数而变化。因子分析表明有两种谱形式的汽车（+）（轿车（a）（+）的吸光度最大为982nm，汽车（b）（+）的吸光度最大为1027nm）衰减在不同的情况下费率。在SyneChocystis PS II中，当氧化酪氨酸D（Y（d）（*））存在于通过Y（d）之间的静电相互作用解释的样品中，观察到较短波长的速率（+）峰值到较短波长的升降波长（ *）和附近的β-胡萝卜素抵御氧化轿车（B）。根据空穴跳跃机制讨论了PS II的二次电子转移路径中的电子转移反应序列，以在低温下达到电荷分离的平衡状态。

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