THE REALITIES OF HOMODIMER-TYPE REACTION CENTER FROM GREEN SULFUR BACTERIA AND ITS OXYGEN SUSCEPTIBILITY

在绿色硫细菌Chlorobium tepidum的反应中心复合物（PS-C）中，A_0和三个Fe-S簇在电子传递链的受体侧起作用，两个cyt c-551分子在供体侧起作用。从多次闪光诱导的光谱学中，我们发现cytc-551在第一次和第二次闪光后的半衰期分别约为60和100 μs。cyt c-551的这些行为可以用两个功能等同的cyt c模型来解释，并且与供体侧的同源二聚体模型一致。上述明显不同的速率是由以下事实解释的：在第一次闪光后，两个cyt c-551可用于向P840提供电子，而在第二次闪光后，大多数PS-C中只有一个cyt c-551可用于向P840提供电子。当PS-C暴露于空气中时，受体侧发生快速失活，实际失活位点有待研究。在PS-C和菠菜FNR存在下，它们都能有效地还原NADP^+。据报道，来自绿色硫细菌的Fds对氧气极其敏感。然而，这些来自C.tepidum的Fds对氧相对不敏感，在4℃有氧条件下储存仅灭活10-15%。我们从运动太阳杆菌中纯化了两个Fds。其中之一是非常敏感的氧气，但其他相对不敏感的氧气是从C. tepidum FDS。

In the reaction center complex (PS-C) from the green sulfur bacterium Chlorobium tepidum, A_0 and three Fe-S clusters function on the accepter side of the electron transfer chain and two molecules of cyt c-551 on the donor side. From multiple-flash-induced spectroscopy, we found that cyt c-551 was reduced with half-lives of about 60 and 100 μs after the first and the second flash, respectively. These behaviors of cyt c-551 are explained by a model of two functionally equivalent cyt c, and are consistent with a homodimeric model on the donor side. The above apparently different rates are explained by the fact that after the first flash, two cyt c-551 are available for electron donation to P840, while only one is available in the majority of PS-C after the second flash. When PS-C was exposed to air, a rapid inactivation occurred on the acceptor side, the actual site of inactivation remaining to be investigated.Four ferredoxins (Fds) of 2[4Fe-4S] type were purified from C.tepidum. In the presence of PS-C and FNR from spinach, all of them supported efficient NADP^+ reduction. Fds from green sulfur bacteria were reported to be extremely sensitive to oxygen. However, these Fds from C.tepidum was relatively insensitive to oxygen, and inactivated by only 10-15% by storage under aerobic conditions at 4℃. We have purified two Fds from Heliobacillus mobilis. One of them was extremely sensitive to oxygen, but the other relatively insensitive to oxygen as are Fds from C.tepidum.