Hoffmann W, Restall C J, Hyla R, Chapman D
Biochim Biophys Acta. 1980 Nov 18;602(3):531-8. doi: 10.1016/0005-2736(80)90332-6.
Bacteriorhodopsin has been reconstituted into lipid vesicles with dipalmitoyl and dimyristoyl phosphatidylcholine. Circular dichroism (CD) measurements show that the proteins are in a monomeric state above the main lipid phase transition temperature (Tc), 41 and 23 degrees C for dipalmitoyl and dimyristoyl phosphatidylcholine, respectively. Below Tc, the CD spectrum is the same as that found for the purple membrane. The latter result implies that the orientation of the chromophore at these temperatures is most likely the same as in the purple membrane (70 degrees +/- 5 degrees from the normal to the membrane plane). Transient dichroism measurements show that below Tc the proteins are immobile, while above this temperature protein rotation around an axis normal to the plane of the membrane is occurring. In addition, from the data the angle of the chromophore for the rotating proteins with respect to the rotational diffusion axis can be calculated. This angle is found to be 30 degrees +/- 3 degrees and 29 degrees +/- 4 degrees in dimyristoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine, respectively. This is considerably smaller than the value of 70 degrees +/- 5 degrees for the natural biomembrane. A reversible reorientation of the chromophore above and below the respective main Tc transition temperature could explain the change of angle observed provided that all the molecules rotate above Tc.
细菌视紫红质已被重组到含有二棕榈酰磷脂酰胆碱和二肉豆蔻酰磷脂酰胆碱的脂质体中。圆二色性（CD）测量表明，在主要脂质相变温度（Tc）以上，蛋白质处于单体状态，二棕榈酰磷脂酰胆碱和二肉豆蔻酰磷脂酰胆碱的Tc分别为41℃和23℃。在Tc以下，CD光谱与紫膜的相同。后一结果表明，在这些温度下，发色团的取向很可能与紫膜中的相同（与膜平面法线成70°±5°）。瞬态二色性测量表明，在Tc以下，蛋白质是不动的，而在该温度以上，蛋白质围绕垂直于膜平面的轴发生旋转。此外，根据这些数据，可以计算出旋转蛋白质的发色团相对于旋转扩散轴的角度。在二肉豆蔻酰磷脂酰胆碱和二棕榈酰磷脂酰胆碱中，该角度分别为30°±3°和29°±4°。这比天然生物膜的70°±5°的值小得多。如果所有分子在Tc以上旋转，发色团在各自主要Tc转变温度上下的可逆重新取向可以解释观察到的角度变化。
