Matsuura K, Hori M, Satoh T
Department of Biology, Faculty of Science, Tokyo Metropolitan University.
J Biochem. 1988 Dec;104(6):1016-20. doi: 10.1093/oxfordjournals.jbchem.a122568.
When cells of the denitrifying phototrophic bacterium Rhodobacter sphaeroides forma sp. denitrificans were grown anaerobically under illumination in the presence of nitrate, the content of photosynthetic reaction centers per cellular protein was less than that in cells grown photosynthetically without nitrate under the same light intensity. The contents of cytochromes c1 and c2, which work in both photosynthetic and denitrifying electron transport systems, were almost constant, being independent of the presence of nitrate during growth. Consequently, the ratio of cytochromes c1 and c2 to the reaction center was more than three in the photo-denitrifying cells, whereas it was close to one in the photosynthetic cells under light-limiting conditions. In spite of the excess of cytochromes c1 + c2 over the reaction center in the photo-denitrifying cells, all cytochromes c1 + c2 were oxidized by illumination within hundreds of milliseconds in the presence of antimycin. When glycerol was added to increase the viscosity in the periplasm, biphasic oxidation of cytochromes c1 + c2 was apparent in the photo-denitrifying cells with repetitive flashes. The fast phase oxidation, which took place instantaneously (less than 1 ms) after the first and second flashes, showed a similar pattern to the oxidation in the light-limiting photosynthetic cells. The rate of the slow phase oxidation was sensitive to viscosity and was thought to reflect a diffusion-controlled second-order reaction between cytochrome c2 and the reaction center. The biphasic oxidation of cytochromes c1 + c2 suggests that these cytochromes exist in the photo-denitrifying cells as two different pools in relation to the reaction center.
当反硝化光合细菌球形红杆菌（Rhodobacter sphaeroides forma sp. denitrificans）的细胞在光照下于硝酸盐存在的条件下厌氧生长时，每细胞蛋白中光合反应中心的含量低于在相同光照强度下无硝酸盐光合生长的细胞中的含量。在光合和反硝化电子传递系统中均起作用的细胞色素c1和c2的含量几乎恒定，与生长过程中硝酸盐的存在无关。因此，在光反硝化细胞中，细胞色素c1和c2与反应中心的比率超过3，而在光限制条件下的光合细胞中该比率接近1。尽管在光反硝化细胞中细胞色素c1 + c2相对于反应中心过量，但在抗霉素存在的情况下，所有细胞色素c1 + c2在光照下数百毫秒内被氧化。当添加甘油以增加周质中的粘度时，在光反硝化细胞中重复闪光时细胞色素c1 + c2出现双相氧化。快速相氧化在第一次和第二次闪光后瞬间（小于1毫秒）发生，显示出与光限制光合细胞中的氧化相似的模式。慢相氧化速率对粘度敏感，被认为反映了细胞色素c2与反应中心之间的扩散控制二级反应。细胞色素c1 + c2的双相氧化表明这些细胞色素在光反硝化细胞中相对于反应中心以两种不同的池存在。
