Wierenga Peter A, Egmond Maarten R, Voragen Alphons G J, de Jongh Harmen H J
Wageningen Centre for Food Sciences, P.O. Box 557, Diedenweg 20, 6700 AN, Wageningen, The Netherlands.
J Colloid Interface Sci. 2006 Jul 15;299(2):850-7. doi: 10.1016/j.jcis.2006.03.016. Epub 2006 Mar 13.
Unfolding of proteins has often been mentioned as an important factor during the adsorption process at air-water interfaces and in the increase of surface pressure at later stages of the adsorption process. This work focuses on the question whether the folding state of the adsorbed protein depends on the rate of adsorption to the interface, which can be controlled by bulk concentration. Therefore, the adsorption of proteins with varying structural stabilities at several protein concentrations was studied using ellipsometry and surface tensiometry. For beta-lactoglobulin the adsorbed amount (Gamma) needed to reach a certain surface pressure (Pi) decreased with decreasing bulk concentration. Ovalbumin showed no such dependence. To verify whether this difference in behavior is caused by the difference in structural stability, similar experiments were performed with cytochrome c and a destabilized variant of this protein. Both proteins showed identical Pi-Gamma, and no dependence on bulk concentration. From this work it was concluded that unfolding will only take place if the kinetics of adsorption is similar or slower than the kinetics of unfolding. The latter depends on the activation energy of unfolding (which is in the order of 100-300 kJ/mol), rather than the free energy of unfolding (typically 10-50 kJ/mol).
在气-水界面的吸附过程以及吸附过程后期表面压力增加期间，蛋白质的去折叠常被提及为一个重要因素。这项工作聚焦于吸附蛋白质的折叠状态是否取决于吸附到界面的速率这一问题，而该速率可通过本体浓度来控制。因此，使用椭偏仪和表面张力测定法研究了在几种蛋白质浓度下具有不同结构稳定性的蛋白质的吸附情况。对于β-乳球蛋白，达到一定表面压力（π）所需的吸附量（Γ）随本体浓度降低而减少。卵清蛋白则未表现出这种依赖性。为了验证这种行为差异是否由结构稳定性差异引起，对细胞色素c及其不稳定变体进行了类似实验。两种蛋白质均表现出相同的π-Γ关系，且不依赖于本体浓度。从这项工作得出的结论是，只有当吸附动力学与去折叠动力学相似或比其慢时，去折叠才会发生。后者取决于去折叠的活化能（约为100 - 300 kJ/mol），而非去折叠的自由能（通常为10 - 50 kJ/mol）。
