title: Zn(2+)-heparin interaction studied by potentiometric titration.
abstract: 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.
authors.affiliation: Department of Molecular and Cell Biology, University of Aberdeen, Marischal College, Scotland, U.K.
authors.forename: D
authors.initials: D
authors.lastname: Grant
authors.forename: W F
authors.initials: WF
authors.lastname: Long
authors.forename: F B
authors.initials: FB
authors.lastname: Williamson
mesh_terms: D001665:Binding Sites; D006493:Heparin / Q000378:metabolism*; D011199:Potentiometry; D015032:Zinc / Q000378:metabolism*
chemical_list: D006493:Heparin; D015032:Zinc