Electron transfer proteins of chloroplast envelope

我们发现在完整的叶绿体照射下，超绿体细胞色素(Cyt)c减少。这一反应不是由基质中产生的可溶性还原剂如超氧化物、过氧化氢或NAD(P)H引起的，而是由跨膜电子转移所介导的。利用还原的细胞色素c的氧化作用，确定了氧化还原物质是一种蛋白质与物质(S)与E^&lt；o1&gt；的多聚体络合物，类似于质体醌。氧化还原物质定位于外膜和内膜，完整叶绿体对Cytc的还原被DCMU抑制，但不被DBMIB抑制，这表明在光合作用的电子传递中，被膜的电子传递接受来自叶绿体中的质醌位置的电子。细胞色素c的加入降低了类囊体膜的二氧化碳固定速率和二氧化碳依赖的放氧率，而分离的被膜抑制了类囊体膜的循环和非循环的光磷化作用。这些光合作用活性的下降并不是电子通过被膜电子转移到Cytc的结果，因为Cytc的减少量远远小于放氧量的减少。被膜电子转移可能是类囊体类囊体和/或叶绿体之间的一种独特的反应，使光合作用的产量相等。

We found the reduction of extrachloroplastic cytochrome (Cyt) c by illuminated intact chloroplasts. This reaction was mediated by a trans-envelope electron transfer but not by soluble reductants generated in stroma such as superoxide, hydrogen peroxide or NAD(P)H.By the use of the oxidation of the reduced Cyt c, re-dox substance was identified as a multimeric complex of proteins with substance (s) with E^<o1> which is similar to that of plastoquinone. The redox substances are localized both in outer and inner envelopes.Cyt c reduction by intact chloroplast was inhibited by DCMU but not by DBMIB which indicates that the envelope electron transfer accepts electrons from the plastoquinone site in the photosynthetic electron transfer. The rates of carbon dioxide fixation and carbon dioxide-dependent oxygen evolution were lowered by the addition of Cyt c. Cyclic and noncyclic photophosphorylations by thylakoid membranes were suppressed by the addition of isolated envelope membranes. These declines in photosynthetic activities were not the result of dissipation of electrons to Cyt c through envelope electron transfer because the reduced amount of Cyt c was much lesser than the decreased yield of oxygen evolution.Envelope electron transfer might be a unique reaction which equalizes the photosynthetic yield between thylakoids and/or chloroplasts.