Szundi I, Stoeckenius W
Proc Natl Acad Sci U S A. 1987 Jun;84(11):3681-4. doi: 10.1073/pnas.84.11.3681.
Purple membrane (lambda max = 568 nm) can be converted to blue membrane (lambda max = 605 nm) by either acid titration or deionization. Partially delipidated purple membrane, containing only 25% of the initial lipid phosphorus, could be converted to a blue form by acid titration but not by deionization. This reversible transition of delipidated membrane did not require the presence of other cations, and the pK of the color change that in native membrane under similar conditions is between 3.0 and 4.0 was shifted to 1.4. We conclude that the purple-to-blue transition is controlled by proton concentration only and that, in native membranes, the cations act only by raising the low surface pH generated by the acidic groups of the lipids. The observation that extraction of lipids from deionized native membrane converts its color from blue to purple further confirms this conclusion. The two states of the membrane probably reflect two preferred conformations of bacteriorhodopsin, which are controlled by protonation changes at the surface of the membrane and differ slightly in the spatial distribution of charges around the chromophore.
紫膜（最大吸收波长λmax = 568 nm）可通过酸滴定或去离子化转化为蓝膜（λmax = 605 nm）。仅含有初始脂质磷25%的部分脱脂紫膜，可通过酸滴定而非去离子化转化为蓝色形式。这种脱脂膜的可逆转变不需要其他阳离子的存在，并且在类似条件下天然膜中颜色变化的pK值在3.0至4.0之间，现转移至1.4。我们得出结论，紫膜到蓝膜的转变仅由质子浓度控制，并且在天然膜中，阳离子仅通过提高由脂质酸性基团产生的低表面pH值起作用。从去离子化天然膜中提取脂质会使其颜色从蓝色变为紫色这一观察结果进一步证实了这一结论。膜的两种状态可能反映了细菌视紫红质的两种优选构象，它们由膜表面的质子化变化控制，并且在发色团周围电荷的空间分布上略有不同。
