Figure. 4.
Approach-to-equilibrium changes in PAI-1 intrinsic protein fluorescence upon mixing with Type I metals. PAI-1 was mixed 1:1 with MgCl2 (A) or MnCl2 (B) in Tris buffer. Changes in intrinsic protein fluorescence emission at wavelengths above 320 nM were monitored continuously for 500 s. After subtraction of background (see Materials and Methods), the data were fit to a double exponential equation with acceptable residuals, represented in the bottom frame below each of the panels. The free metal concentration was calculated from the total metal concentration and the buffer/metal affinity constant (see Materials and Methods).