Grant D, Long W F, Williamson F B
Department of Molecular and Cell Biology, University of Aberdeen, Marischal College, Scotland, U.K.
Biochem J. 1992 Nov 1;287 ( Pt 3)(Pt 3):849-53. doi: 10.1042/bj2870849.
Measurement of the decrease in pH that accompanies the addition of Zn2+ to heparin in solution provided an indirect method of examining cation-polyanion interaction. Construction of plots analogous to isothermal saturation binding plots revealed the existence, for defined conditions of interaction, of a [heparin]-independent direct proportionality between the fraction of the maximal pH change occurring and the [Zn2+]/[heparin disaccharide] ratio. This accords with results from polarimetric examination of Ca(2+)- and Cu(2+)-heparin interactions. It suggests that, under the conditions used, cation-heparin interaction may result in the formation of a complex that exists in a colloid-like phase, between which and the aqueous phase, exchange of cations does not follow simple solution-phase reversible equilibrium thermodynamic behaviour. The results suggest that the putative Zn(2+)-containing complex is less stable in the presence of NaCl than is the corresponding Ca(2+)-containing complex. Addition of Zn2+ to low concentrations of heparins is accompanied by the usual decrease in pH, followed by a removal of H+ from solution as the [Zn2+]/[heparin disaccharide] ratio increases, suggesting dissolution of the putative complex. This reversal of the initial pH change was not seen for most other cation-heparin interactions under the conditions studied.
测量向溶液中的肝素添加Zn2+时伴随的pH值下降，提供了一种检测阳离子-阴离子相互作用的间接方法。构建类似于等温饱和结合曲线的曲线表明，在特定的相互作用条件下，发生的最大pH变化分数与[Zn2+]/[肝素二糖]比率之间存在与[肝素]无关的直接比例关系。这与对Ca(2+)-和Cu(2+)-肝素相互作用进行旋光测定的结果一致。这表明，在所使用的条件下，阳离子-肝素相互作用可能导致形成一种存在于胶体状相中的复合物，在该相和水相之间，阳离子的交换并不遵循简单的溶液相可逆平衡热力学行为。结果表明，假定的含Zn(2+)复合物在NaCl存在下比相应的含Ca(2+)复合物稳定性更低。向低浓度肝素中添加Zn2+会伴随着通常的pH值下降，随后随着[Zn2+]/[肝素二糖]比率的增加，H+从溶液中去除，这表明假定的复合物溶解。在所研究的条件下，大多数其他阳离子-肝素相互作用未见初始pH变化的这种逆转。
