Su TJ, Lu JR, Thomas RK, Cui ZF, Penfold J
Department of Chemistry, University of Surrey, Guildford, GU2 5XH, United Kingdom
J Colloid Interface Sci. 1998 Jul 15;203(2):419-29. doi: 10.1006/jcis.1998.5545.
The adsorption of lysozyme (chicken egg white) from aqueous solution on to the hydrophilic silica surface and the variation of interfacial structure with solution conditions have been studied by neutron reflection. The accurate determination of the adsorbed layer thicknesses in combination with the dimension of the globular structure of lysozyme allows us to postulate the mean structural conformation of the lysozyme molecules within the adsorbed layer. It was found that the adsorption was completely reproducible with respect to lysozyme concentration, but it was irreversible. The effect of ionic strength on the adsorption of lysozyme was examined at pH 7 and at a bulk lysozyme concentration of 0.03 g dm-3. The adsorbed layer was not affected by changes in ionic strength when the total ionic strength was below 0.05 M, but above this concentration addition of NaCl gradually reduced the amount of lysozyme adsorbed. Complete removal of adsorbed lysozyme was achieved when the total ionic strength was above 0.5 M. The effect of solution pH on the amount of lysozyme adsorbed was characterized by varying the pH in cycles at fixed lysozyme concentrations. Adsorption was found to be completely reversible with respect to pH over a wide protein concentration range. The level of surface excess was dominated by the electrostatic repulsion between lysozyme molecules within the adsorbed layers, rather than the attraction between the surface and lysozyme. The lysozyme layer structure along the surface normal was characterized by varying the isotopic composition of the water. At pH 7 a monolayer 30 +/- 2 Å thick was formed when the lysozyme concentration was below 0.03 g dm-3, indicating that the lysozyme was adsorbed with its long axis parallel to the surface (sideways-on). At higher concentrations the thickness of the layer changed to 60 +/- 2 Å, suggesting the formation of a bilayer of lysozyme molecules in the sideways-on configuration. When the lysozyme concentration is above 1 g dm-3 the surface excess within the inner layer is sufficiently high that repulsion within the adsorbed layer becomes significant and the molecules start to tilt towards longways-on adsorption. At pH 4, the electrostatic repulsion between the adsorbed molecules is stronger than at pH 7, resulting in a lower surface excess and a tilting away from the sideways-on configuration at lower surface concentration. Copyright 1998 Academic Press.
通过中子反射研究了溶菌酶（鸡蛋白）从水溶液吸附到亲水性二氧化硅表面以及界面结构随溶液条件的变化。准确测定吸附层厚度并结合溶菌酶球状结构的尺寸，使我们能够推测吸附层内溶菌酶分子的平均结构构象。发现吸附对于溶菌酶浓度而言完全可重现，但却是不可逆的。在pH 7和本体溶菌酶浓度为0.03 g dm⁻³的条件下，研究了离子强度对溶菌酶吸附的影响。当总离子强度低于0.05 M时，吸附层不受离子强度变化的影响，但高于此浓度时，添加氯化钠会逐渐减少溶菌酶的吸附量。当总离子强度高于0.5 M时，可实现对吸附溶菌酶的完全去除。通过在固定溶菌酶浓度下循环改变pH值，表征了溶液pH值对溶菌酶吸附量的影响。发现在较宽的蛋白质浓度范围内，吸附对于pH值而言是完全可逆的。表面过量水平主要由吸附层内溶菌酶分子之间的静电排斥作用决定，而非表面与溶菌酶之间的吸引力。通过改变水的同位素组成，表征了沿表面法线方向的溶菌酶层结构。在pH 7时，当溶菌酶浓度低于0.03 g dm⁻³时，形成了厚度为30±2 Å的单层，这表明溶菌酶以其长轴平行于表面的方式（侧向）吸附。在较高浓度下，层的厚度变为60±2 Å，表明形成了侧向构型的溶菌酶分子双层。当溶菌酶浓度高于1 g dm⁻³时，内层的表面过量足够高，以至于吸附层内的排斥作用变得显著，分子开始向纵向吸附倾斜。在pH 4时，吸附分子之间的静电排斥作用比在pH 7时更强，导致表面过量更低，并且在较低表面浓度下偏离侧向构型。版权所有1998年学术出版社。
