Lechner R E, Fitter J, Dencher N A, Hauss T
Hahn-Meitner-Institut/BENSC, Glienicker Strasse 100, Berlin, D-14109, Germany.
J Mol Biol. 1998 Apr 3;277(3):593-603. doi: 10.1006/jmbi.1997.1597.
The lamellar spacing dl of purple membrane (PM) multilayer systems was investigated with neutron diffraction as a function of temperature and of the level of hydration. The observed large T-dependent variations of dl indicate that PM is partially dehydrated when cooled below a "hydration water freezing point". This phenomenon is reversible, but a hysteresis is observed when PM is rehydrated upon reheating. The hydration water remaining bound to the membrane below about 240 K is non-freezing. Its amount was found to be hnf=0.24(+/-0.02) g 2H2O/g BR for all samples equilibrated at room temperature in the presence of 2H2O vapour at >/=84% r.h. It is evident, that the dehydration/rehydration behaviour of PM is strongly correlated with the temperature-dependent behaviour of the dynamical structure factor. Above the well-known "dynamical transition" announcing the onset of localized diffusive molecular motions between 190 K and 230 K, a second dynamical transition is caused by the temperature-induced rehydration of the PM starting near 255 K. This is also correlated with the deviation from a pure Arrhenius law of the rate-limiting process in the photocycle, known to occur upon cooling beyond the ice point into the same temperature region. Our results suggest that the phenomenon of dehydration and rehydration induced by cooling and reheating, respectively, is a general property of biological membranes.
利用中子衍射研究了紫膜（PM）多层系统的层间距dl随温度和水合水平的变化。观察到的dl随温度的大幅变化表明，当冷却至“水合水冰点”以下时，PM会部分脱水。这种现象是可逆的，但当PM在重新加热时再水化时会观察到滞后现象。在约240 K以下仍与膜结合的水合水不结冰。对于在相对湿度≥84%的2H2O蒸汽中于室温下平衡的所有样品，发现其含量为hnf = 0.24（±0.02）g 2H2O/g BR。显然，PM的脱水/再水化行为与动态结构因子的温度依赖性行为密切相关。在190 K至230 K之间宣布局部扩散分子运动开始的著名的“动态转变”之上，第二个动态转变是由PM在接近255 K时温度诱导的再水化引起的。这也与光循环中限速过程偏离纯阿伦尼乌斯定律有关，已知在冷却至冰点以下进入相同温度区域时会发生这种情况。我们的结果表明，分别由冷却和再加热引起的脱水和再水化现象是生物膜的普遍特性。
