Lill H, Junge W
Biophysik, Fachbereich Biologie/Chemie, Universität Osnabräuck, Federal Republic of Germany.
Eur J Biochem. 1989 Feb 1;179(2):459-67. doi: 10.1111/j.1432-1033.1989.tb14575.x.
The discharge of the flash-induced transmembrane voltage through the exposed proton channel, CF0, of the chloroplast ATP synthase, CF0CF1 was investigated. EDTA treatment of thylakoid membranes exposed approximately 50% of total CF0 by removal of the CF1 counterparts. This greatly accelerated the decay of the transmembrane voltage, as was apparent from electrochromic-absorption changes of intrinsic pigments and by pH-indicating-absorption changes of added dyes. Two decay processes were discernible, one rapid with a typical half-decay time of 2 ms, and a slower one with a half-decay time variable between 20-100 ms. Both were sensitive to CF0 inhibitors, but only the rapid decay process was also inhibited by added CF1. CF1 was effective in surprisingly small amounts, which were significantly lower than those previously removed by EDTA treatment. This finding corroborated our previous conclusion that the rapid decay of the transmembrane voltage was attributable to only a few high-conductance channels among many CF0 molecules, typically in the order of one channel/CF1-depleted EDTA vesicle. Inhibition of photophosphorylation in control thylakoids was measured as function of the concentration of CF0 inhibitors. It was compared with the inhibition of proton conduction through exposed CF0 in EDTA vesicles. Photophosphorylation and proton conduction by the high-conductance form of CF0 were inhibited by the same low inhibitor concentrations. This suggested that the high-conducting form of CF0 with a time-averaged single-channel conductance of 1 pS [Lill, H., Althoff, G. & Junge, W. (1987) J. Membrane Biol. 98, 69-78] represented the proton channel in the integral enzyme, which acted as a low-impedance access from the thylakoid lumen to the coupling site in CF0CF1. The slow decay process was attributed to a majority of low-conductance CF0 channels, i.e. about 50 molecules/vesicle. The conductance of these channels was more than 100-fold lower and they did not compete with the very few highly conducting channels for rebinding of added CF1. The low proton conduction of the majority of exposed CF0 molecules, possibly due to a structural rearrangement, may be protecting the thylakoid membrane against rapid energy dissipation caused by accidental loss of CF1. It may also explain the low single-channel conductance of bacterial F0 reported in the literature.
对叶绿体ATP合酶CF0CF1中通过暴露的质子通道CF0的闪光诱导跨膜电压放电进行了研究。用乙二胺四乙酸（EDTA）处理类囊体膜，通过去除CF1对应物，使约50%的总CF0暴露出来。这极大地加速了跨膜电压的衰减，这从内在色素的电致变色吸收变化以及添加染料的pH指示吸收变化中可以明显看出。可以辨别出两个衰减过程，一个快速过程，典型的半衰期为2毫秒，另一个较慢过程，半衰期在20 - 100毫秒之间变化。两者都对CF0抑制剂敏感，但只有快速衰减过程也受到添加的CF1的抑制。CF1只需极少量就有效，这一量明显低于先前用EDTA处理去除的量。这一发现证实了我们之前的结论，即跨膜电压的快速衰减仅归因于许多CF0分子中的少数高电导通道，通常为每个CF1缺失的EDTA囊泡一个通道左右。在对照类囊体中，光磷酸化的抑制作用作为CF0抑制剂浓度的函数进行测量。将其与通过EDTA囊泡中暴露的CF0的质子传导抑制作用进行比较。光磷酸化和CF0高电导形式的质子传导受到相同低抑制剂浓度的抑制。这表明CF0的高电导形式，其时间平均单通道电导为1皮安[利尔，H.，阿尔托夫，G. & 荣格，W.（1987年）《膜生物学杂志》98，69 - 78]，代表了完整酶中的质子通道，它作为从类囊体腔到CF0CF1中偶联位点的低阻抗通道。缓慢衰减过程归因于大多数低电导CF0通道，即每个囊泡约50个分子。这些通道的电导低100倍以上，并且它们不会与极少数高电导通道竞争添加的CF1的重新结合。大多数暴露的CF0分子的低质子传导，可能是由于结构重排，可能在保护类囊体膜免受因CF1意外丢失而导致的快速能量耗散。这也可能解释了文献中报道的细菌F0的低单通道电导。
