Table 1.

pH dependence of McGhee-von Hippel logK_obs and SK_obs as a function of amino acid composition

pH	logKobsa	SKobsb	logK0b (1 M Na+)	Qmaxc (%)
	KWKK (24.4 mM Na+)
5.2	5.06 ± 0.02	−3.06 ± 0.09	0.10 ± 0.12	0.91 ± 0.01
6.0	4.88 ± 0.01	−3.05 ± 0.06	0.01 ± 0.09	0.91 ± 0.01
7.0	4.69 ± 0.02	−2.94 ± 0.06	−0.06 ± 0.08	0.91 ± 0.02
8.0	4.16 ± 0.01	−2.59 ± 0.06	−0.01 ± 0.09	0.91 ± 0.02
8.7	3.77 ± 0.02	−2.45 ± 0.11	−0.13 ± 0.17	0.87 ± 0.01d
	HWKK (9.8 mM Na+)
5.2	5.98 ± 0.02	−2.84 ± 0.10	0.25 ± 0.15	0.92 ± 0.02
6.0	5.23 ± 0.02	−2.55 ± 0.09	0.09 ± 0.12	0.93 ± 0.01
7.0	4.59 ± 0.02	−2.21 ± 0.06	0.11 ± 0.11	0.93 ± 0.01
8.0	3.83 ± 0.02	−1.93 ± 0.07	−0.01 ± 0.12	0.88 ± 0.01e
8.7	3.38 ± 0.02	−1.64 ± 0.13	0.14 ± 0.24	0.81 ± 0.02e

^aDetermined by global nonlinear least squares analysis of data collected at 25 °C across multiple oligopeptide concentrations at the specified salt concentration using the noncooperative McGhee-von Hippel equation (eq. 1) with the indicated Q_max and n = 5. Errors represent 95% confidence intervals.

^bSK_obs and logK₀ values were calculated by nonlinear least squares analysis of aggregate logK_obs versus [Na⁺] data from reverse titrations and saltbacks. Saltback logK_obs data were obtained using the indicated Q_max and n = 5 via eq. 1 – 4.

^cCalculated via model-independent ligand binding density analysis (42) of reverse titration data at the specified salt concentration.

^dWhen binding was weaker than K_obs ≲ 10⁴ M⁻¹, Q_max was found by ligand binding density analysis using data collected at the same pH but lower salt concentration to improve the accuracy of the determination (cf. Figure S1). At high pH, Q_max is reported at 12.4 mM Na⁺ for KWKK

^eWhen binding was weaker than K_obs ≲ 10⁴ M⁻¹, Q_max was found by ligand binding density analysis using data collected at the same pH but lower salt concentration to improve the accuracy of the determination (cf. Figure S1). At high pH, Q_max is reported at 5.4 mM Na⁺ for HWKK.