Department of Chemical and Geological Sciences, University of Cagliari-CSGI and CNBS, Cittadella Universitaria , S.S. 554 bivio Sestu, 09042 Monserrato (CA), Italy.
Langmuir. 2013 Dec 10;29(49):15350-8. doi: 10.1021/la404249n. Epub 2013 Nov 25.
Turbidity titrations are used to study the ion specific aggregation of hemoglobin (Hb) below and physiological salt concentration in the pH range 4.5-9.5. At a salt concentration 50 mM cations promote Hb aggregation according to the order Rb(+) > K(+) ~ Na(+) > Cs(+) > Li(+). The cation series changes if concentration is increased, becoming K(+) > Rb(+) > Na(+) > Li(+) > Cs(+) at 150 mM. We interpret the puzzling series by assuming that the kosmotropic Li(+) will bind to kosmotropic carboxylates groups-according to the law of matching water affinities (LMWA)-whereas the chaotropic Cs(+) will bind to uncharged protein patches due to its high polarizability. In fact, both mechanisms can be rationalized by invoking previously neglected ionic nonelectrostatic forces. This explains both adsorption to uncharged patches and the LMWA as a consequence of the simultaneous action of electrostatic and dispersion forces. The same interpretation applies to anions (with chaotropic anions binding to chaotropic amine groups). The implications extend beyond hemoglobin to other, still unexplained, ion specific effects in biological systems.
浊度滴定法用于研究血红蛋白 (Hb) 在生理盐浓度以下和 pH 值 4.5-9.5 范围内的离子特异性聚集。在盐浓度为 50mM 时，阳离子根据 Rb(+) > K(+) ~ Na(+) > Cs(+) > Li(+)的顺序促进 Hb 聚集。如果增加浓度，阳离子系列会发生变化，在 150mM 时变为 K(+) > Rb(+) > Na(+) > Li(+) > Cs(+)。我们通过假设具有亲溶性质的 Li(+) 将与亲溶的羧酸盐基团结合（根据水亲和力匹配规律，即 LMWA），而具有高极化率的 Cs(+) 将与不带电荷的蛋白质斑块结合，从而解释了令人困惑的系列。实际上，这两种机制都可以通过调用以前被忽视的离子非静电相互作用来合理化。这不仅解释了对不带电荷斑块的吸附，也解释了 LMWA 是由于静电和色散力的同时作用的结果。同样的解释也适用于阴离子（具有亲溶性质的阴离子与亲溶的胺基团结合）。这种解释不仅适用于血红蛋白，也适用于生物系统中其他尚未解释的离子特异性效应。
