Binding of high affinity heparin to antithrombin III. Stopped flow kinetic studies of the binding interaction.

The kinetics of high affinity heparin binding to human antithrombin III has been studied by stopped flow fluorimetry, using the 40% antithrombin fluorescence enhancement resulting from this interaction.At p 0.15, pH 7.4, and 25 "C, the observed pseudo-first order rate constant varies hyperbolically with heparin concentration with a limiting rate constant of 440 & 90 s-', demonstrating that heparin binding is a two-step process involving a conformational change in antithrombin