Table 1.

Values of kinetic and thermodynamic parameters for the binding of o₂ and of the endogenous ligand HisE7 to ferrous human NGB and CYGB

Globin	Ligand	kona	koff (S−1)	K′(L)b(M−1)	P50′c(torr)	p50*d(torr)
NGBe	O2	2.5 × 108 M−1 s−1	0.80	7.0 × 105	0.79	1
NGBf	O2	1.3 × 108 M−1 S−1	0.30	2.0 × 108	2.8 × 10−3	–
CYGBg	O2	3.0 × 107 M−1 s−1	0.35	1.0 × 106	0.55	–
NGBe	HisE7	2.0 × 103 s−1	4.5	–	–	–
NGBf	HisE7	9.8 × 103 s−1	8.2 × 103	–	–	–
CYGBg	HisE7	4.3 × 102 s−1	5	–	–	–

^aValues of K′_(on) differ in their units depending on whether the heme-Fe ligand is endogenous (i.e. HisE7, s⁻¹) or exogenous (i.e. O₂ or CO, M⁻¹ s⁻¹).

^bValues of K′_(L) were calculated according to the following equation (Trent et al., 2001):

.

^cValues of P₅₀′ were calculated according to the following equation:

, where A (= 1.38 × 10⁻³ M) is the O₂ solubility in water at 760 torr, pH 7.0 and 20.0°C (Antonini and Brunori, 1971).

^dThe value of P₅₀* was determined from equilibrium experiments.

^eData from Burmester et al. (2000); Dewilde et al. (2001).

^fTrent et al. (2001).

^gTrent and Hargrove (2002).