Table 2.

Hemin dissociation constants and m-values for the NH and IH states of holo-metMb variants¹.

HoloMb Variant	KNH0 (M)	mNH kcal mol−1 M−1	KIH0 (M)	mIH kcal mol−1 M−1	K-H pH 7–82 (M)	K-H pH 52 (M)
WT	0.88 × 10−13	4.4	1.4 × 10−11	4.0	0.28 × 10−13	28 × 10−13
H64F	4.1 × 10−13	3.5	1.0 × 10−11	3.3	2.2 × 10−13	130 × 10−13
T67P	1.0 × 10−13	4.3	3.6 × 10−11	2.8	n.d.	n.d.
V68T	0.016 × 10−13	4.1	1.5 × 10−11	3.2	≤0.05 × 10−13	1.1 × 10−13
H97D	84 × 10−13	3.4	8.8 × 10−11	2.4	180 × 10−13	1100 × 10−13

¹The unfolding measurements were carried out in 0.01 M potassium phosphate pH 7, 20 °C. K_UH⁰ and m_UH were fixed to 1.0 × 10⁻⁶ M and 2.4 kcal mol⁻¹ M⁻¹, respectively, for all five variants as described in DISCUSSION. The CD, fluorescence, and Soret absorbance signal parameters are given in Table S2 of the Supplementary Material.

²The values for K_-H were computed from the hemin dissociation rate constants assuming that the association rate constant is 1.0 × 10⁸ M⁻¹ s⁻¹ for all five variants, as described in Hargrove et al. (30). The dissociation rate constants were taken from data at pH 7 and pH 5 at 37 °C in 0.45 M sucrose and 0.15 M sodium phosphate or acetate, respectively (22, 29). Unfortunately, the dissociation rate constant for H64F at pH 7 reported in Hargrove et al. (29) is a misprint (i.e., the real value is 0.1 h⁻¹ and not 0.01 h⁻¹). We used the value of 0.08 h⁻¹, which was measured in Hargrove et al. (39). n.d., not determined.