酶切菌紫质(bR)C端对紫膜光循环和质子泵效率的影响

本文研究紫膜悬浮液经低剂量木瓜蛋酶处理去掉菌紫质(Bacteriorhodopsin简写bR)分子C-末端后。其光循环产物和质子泵效率的变化。实验发现经酶切后,M_(412)产物中慢衰减组份M_(412)降低了20％,O_(640)降低了50％,而质子泵效率降低了70％。双光脉冲实验表明酶解作用并不影响光循环周期。这些事实说明了去C-端所引起的质子泵效率降低,不是通过光循环的途径而产生的。介质中离子强度对正常紫膜和酶解紫膜的质子泵效率有明显不同的影响 说明了C端在不同盐浓度中的构象对质子泵行为有很重要的作用。

EFFECTS OF THE REMOVAL OF THE CARBOXYL TERMINAL TAIL OF BACTERIORHODOPSIN(BR) BY PAPAIN DIGESTION ON THE PHOTOCYCLE AND PROTON PUMPING

The photocycle characteristics and proton pumping efficiency of purpleme-mbrane suspension with the C-terminal of BR digested by papain proteolysis in low salt concentration were studied. It was found that the slow dcay component M5 of intermediate Mm was reduceb dy 20%, the intermediate O640 by 50%, and the proton pumping efficiency was reduced by 70%.The response to the second flash after a first flash in a different time gap showed that the period of photocycle did not change. All these results indicate that the proton pumping efficiency change caused by the enzyme digestion dosen't coinc'de with hte photocycle intermediate change.The ionic strength has different influences on normal and papain-treated purple membrane. It suggests that there is a different conformation of C-terminal which is essential for proton pumping in different salt concentration.