共查询到2条相似文献,搜索用时 0 毫秒
1.
The phase transition of the purple membrane observed by differential scanning calorimetry (Jackson, M.B. and Sturtevant, J.M. (1978) Biochemistry 17, 911–915) has been investigated by X-ray diffraction, circular dichroism and absorption spectrum, in comparison with the phase transition in the brown holo-membrane. The two-dimensional crystal of bacteriorhodopsin transformed into two-dimensional liquid around 74–78°C in the purple membrane and around 50–60°C in the brown holo-membrane. The X-ray diffraction patterns obtained at 78°C for the purple membrane and at 60°C for the brown holo-membrane exhibit several broad peaks. Analysis of the pattern suggests that bacteriorhodopsin molecules aggregate in trimers even above the phase transition temperature. The negative circular dichroism band in the visible region is still present at 80°C in the purple membrane and at 60°C in the brown holo-membrane, but becomes negligibly small at 70°C in the brown holo-membrane. The 560 nm absorption peak due to bacteriorhodopsin changes its position and height drastically around 80°C in the brown holo-membrane as in the purple membrane. X-ray diffraction studies have been made on membranes of total lipids extracted from the purple membrane. No indication of the phase transition has been found between ?81°C and 77°C. 相似文献
2.
The interrelation was studied between the phototransient absorbing maximally at 412 nm (M412) and light-induced proton release under steady-state conditions in aqueous suspensions of ‘purple membrane’ derived from Halobacterium halobium. The decay of M412 was slowed down by the simultaneous application of the ionophoric antibiotics valinomycin and beauvericin. The former had only slight activity alone and the latter was effective only in conjunction with valinomycin. The steady-state concentration of M412 which was formed on illumination was a direct function of the concentration of valinomycin. Maximum stabilization of M412 was obtained when the valinomycin was approximately equimolar with the bacteriorhodopsin. Addition of salts to the medium increased the number of protons released per molecule of M412 without affecting the level of M412 which was produced by continuous illumination. The effectiveness of the salts in this respect depended on the nature of the cation. Ca2+ and their antagonists La3+ and ruthenium red were found to have especially high affinity for the system. The extent of light-induced acidification could not be enhanced by increasing the pH of the medium from 6.5 to 7.8. The possible mechanism of action of the ionophores and of the cations on the photocycle and on the proton cycle is discussed. 相似文献