Table 2.

Summary of midpoint concentrations.

	Urea		GdnHCl
	1 h	24 h	1 h	24 h
ZnLF	1.89 (±0.06)	1.55 (±0.03)	0.68 (±0.06)	0.49 (±0.01)
apoLF	1.65 (±0.04)	1.33 (±0.05)	0.65 (±0.08)	0.51 (±0.01)
	2.45 (±0.08)	2.43 (±0.02)
apoLF+Zn2+	1.97 (±0.01)	1.67 (±0.03)	n.d.	n.d.

n.d., not determined. All values (expressed in mol L⁻¹) represent the mean (±1 s.d.) of at least three independent experiments, and were calculated (using Eq. (3)) from the $\mathrm{\Delta }{G}^0$ and m parameters obtained (for each unfolding profile) by fitting of the recorded fluorescence intensities (FI₃₃₃) to Eqs. (1) and/or (2). While values recorded after 24 h of exposure to urea or GdnHCl denote thermodynamic midpoint concentrations, those obtained after 1 h of incubation represent apparent $C^{mid}$ values in view of the lack of a fully established equilibrium after this period of time. Except for urea-denatured apoLF (after both 1 h and 24 h of exposure), the best fit was obtained using the two-state model (see Eq. (1)), with the shown midpoint concentration representing $C_{N\to U}^{mid}$. In the case of urea-exposed apoLF, the best fit was obtained with Eq. (2) (three-state model), yielding $C_{N\to I}^{mid}$ (first value) and $C_{I\to U}^{mid}$ (second value).