Hunter C N, Holmes N G, Jones O T, Niederman R A
Biochim Biophys Acta. 1979 Nov 8;548(2):253-66. doi: 10.1016/0005-2728(79)90133-6.
Previous pulse-chase studies have shown that bacteriochlorophyll a-protein complexes destined eventually for the photosynthetic (chromatophore) membrane of Rhodopseudomonas sphaeroides appear first in a distinct pigmented fraction. This rapidly labeled material forms an upper band when extracts of phototrophically grown cells are subjected directly to rate-zone sedimentation. In the present investigation, flash-induced absorbance changes at 605 nm have demonstrated that the upper fraction is enriched two-fold in photochemical reaction center activity when compared to chromotophores; a similar enrichment in the reaction center-associated B-875 antenna bacteriochlorophyll complex was also observed. Although b- and c-type cytochromes were present in the upper pigmented band, no photoreduction of the b-type components could be demonstrated. The endogenous c-type cytochrome (Em = +345 mV) was photooxidized slowly upon flash illumination. The extent of the reaction was increased markedly with excess exogenous ferrocytochrome c but only slightly in chromatophores. Only a small light-induced carotenoid band shift was observed. These results indicate that the rapidly labeled fraction contains photochemically competent reaction centers associated loosely with c-type and unconnected to b-type cytochrome. It is suggested that this fraction arises from new sites of cytoplasmic membrane invagination which fragment to form leaky vesicles upon cell disruption.
先前的脉冲追踪研究表明，最终定位于球形红假单胞菌光合（载色体）膜的细菌叶绿素a-蛋白复合物首先出现在一个独特的色素部分中。当将光合生长细胞的提取物直接进行速率区沉降时，这种快速标记的物质形成一条上带。在本研究中，605nm处的闪光诱导吸光度变化表明，与载色体相比，上层部分的光化学反应中心活性富集了两倍；在与反应中心相关的B-875天线细菌叶绿素复合物中也观察到了类似的富集。尽管上层色素带中存在b型和c型细胞色素，但未证明b型成分有光还原现象。内源性c型细胞色素（Em = +345 mV）在闪光照射下缓慢发生光氧化。用过量的外源亚铁细胞色素c时，反应程度显著增加，但在载色体中仅略有增加。仅观察到一个小的光诱导类胡萝卜素带位移。这些结果表明，快速标记的部分含有与c型细胞色素松散相关且与b型细胞色素不相连的具有光化学活性的反应中心。有人认为，这一部分来自细胞质膜内陷的新位点，在细胞破碎时这些位点会断裂形成渗漏小泡。
