Binding of Zn²⁺ to HRG monitored by SPR. Biotin-HRG was immobilized on a streptavidin-modified chip to 800 RU. ZnCl₂ (0-10 000nM) was injected over the flow cell for 120 seconds, and then buffer was injected. ZnCl₂ concentrations in nanomolar are noted beside each tracing. (Inset) A plot of the RU values at equilibrium versus the concentration of ZnCl₂. The data were analyzed by rectangular hyperbola equation (line).