Determination of strontium binding to macromolecules

An equilibrium dialysis technique for determining the binding of strontium to macromolecules is described. The major difficulty to be overcome is that 90Sr has a decay product, 90Y, which is also a beta-emitter. The described protocol is used to determine the Sr binding isotherm to bovine prothrombin fragment 1. The binding is found to be cooperative, somewhat weaker than Ca binding, and to involve approximately nine strontium sites. The stoichiometric equilibrium constants are determined by nonlinear regression. The procedure should be of great utility for many macromolecules that show strontium affinity.