. 2010 Dec 29;286(12):10515–10529. doi: 10.1074/jbc.M110.176271

TABLE 2.

Comparison of wild type, Gly(E7), and Trp(E7) association rate constants for CO and O₂ binding to isolated HbA subunits and Mb

Globin and conformer	k′_CO	Open → closed, blocked	k′_O₂	k′_entry
	μm⁻¹s⁻¹	s⁻¹	μm⁻¹s⁻¹	μm⁻¹s⁻¹
His(E7) α	5.5^a	≥1,400,000^b	40^a	36^a
Gly(E7) α	100^a	NA^c	250^a	150^a

Trp(E7) α
Open	92		210^a,d	160^a
Closed	0.12	18,000	∼0.5^a	0.14^a
His(E7) β	7.2^a	≥1,400,000^b	52^a	42^a
Gly(E7) β	40^a	NA	160^a	89^a

Trp(E7) β
Open	80		130^d	250^a
Blocked	0.7	130,000	1.7^a	1.2^a
Closed	0.06	50,000		0.13^a
His(E7) Mb	0.51^e	1,400,000^b	17^e	34^f
Gly(E7) Mb	5.8^e	NA	140^e	540^f
Trp(E7) Mb	0.70	NA	6.2^e	8.6^f

^a Rate parameter taken from Birukou et al. (35).

^b The interconversion rate for Mb was taken from Tian et al. (65, 66); corresponding parameters for Hb subunits were assumed to be equal to or larger than that for Mb (see “Discussion”).

^c NA, not applicable.

^d Computed as the slope of the linear dependence of the observed rate on [ligand].

^e Rate parameter taken from Springer et al. (81).

^f Rate parameter taken from Scott et al. (34).