Table 3. Thermodynamic parameters for the disorder ↔ α-helix transition within the MBP α₂-peptides in aqueous conditions.

α2-peptide variant	a[TFE]mid (M)	bΔ[TFE]mid (M)	cΔGH2O (kJ/mole)	dΔΔGH2O (kJ/mole)
Unmodified	2.31±0.07	n.a	14.9±0.5	en.a
PhT92	2.65±0.09	0.3	17.2±0.6	+2.2
PhT95	2.53±0.10	0.2	16.4±0.7	+1.4
PhT92–PhT95	2.69±0.03	0.4	17.4±0.2	+2.5

Thermodynamic values were determined at 25°C from fitting CD-monitored TFE-titration curves to a 2-state transition (disordered↔α-helical). All errors (±) are standard deviations from at least three independent experiments.

^a[TFE]_mid was determined from data fitting and represents the [TFE] at the mid-point of the transition (i.e., [TFE] when half the peptide molecules contain an α-helical conformation).

^bΔ[TFE]_mid = [TFE]_mid (phosphorylated peptide)−[TFE]_mid (unmodified peptide).

^cΔG^H2O is the change in free energy of the transition calculated as ΔG^H2O = [TFE]_mid•m; where m is the dependence of ΔG on [TFE], determined directly by independently fitting all titration curves (both modified and phosphorylated) and averaging to yield a value of 6.5±0.7 kJ mole⁻¹ M⁻¹.

^dΔΔG^H2O = ΔG^H2O (phosphorylated peptide) − ΔG^H2O (unmodified peptide).

^en.a, not applicable.