Lehrmann R, Seelig J
Department of Biophysical Chemistry, Biocenter of the University of Basel, Switzerland.
Biochim Biophys Acta. 1994 Jan 3;1189(1):89-95. doi: 10.1016/0005-2736(94)90284-4.
The adsorption of Ca2+ and La3+ ions to the surface of lipid bilayer membranes was studied with high sensitivity titration calorimetry. Ca2+ adsorbs to mixed phosphatidylcholine/phosphatidylglycerol membranes with a reaction enthalpy of delta H approximately 0.1-0.2 kcal/mol. La3+ binds to sonified phosphatidylcholine vesicles with a reaction enthalpy of delta H approximately +1.8 kcal/mol. Adsorption of La3+ to phosphatidylcholine bilayers imparts a net positive charge to the membrane surface which makes the binding of further La3+ increasingly more difficult. From the decreasing amplitudes in the calorimetric titration experiment a La3+ adsorption constant of K approximately (4.1 +/- 1.1) x 10(3) M-1 was evaluated. Electrostatic effects were corrected for by means of the Gouy-Chapman theory. The adsorption constant of Ca2+ was determined previously as K approximately 10-20 M-1 using the same binding model. Since the reaction enthalpies of Ca2+ and La3+ adsorption are endothermic, the adsorption of both metal ions to the membrane surface is driven by a distinct change in entropy.
采用高灵敏度滴定热法研究了Ca2+和La3+离子在脂质双分子层膜表面的吸附情况。Ca2+吸附到混合磷脂酰胆碱/磷脂酰甘油膜上，反应焓ΔH约为0.1 - 0.2 kcal/mol。La3+与超声处理的磷脂酰胆碱囊泡结合，反应焓ΔH约为 +1.8 kcal/mol。La3+吸附到磷脂酰胆碱双分子层上会使膜表面带上净正电荷，这使得进一步吸附La3+变得越来越困难。从量热滴定实验中逐渐减小的幅度，评估出La3+的吸附常数K约为(4.1 ± 1.1)×10³ M⁻¹。借助古依 - 查普曼理论校正了静电效应。使用相同的结合模型，先前测定Ca2+的吸附常数K约为10⁻²⁰ M⁻¹。由于Ca2+和La3+吸附的反应焓是吸热的，两种金属离子在膜表面的吸附是由熵的显著变化驱动的。
