Table 1.

Kinetics and equilibrium constants for the reactions of ferrous HbN with oxygen and carbon monoxide compared to those of other proteins

Protein	Oxygen				Carbon Monoxide
	k′on, μM−1·s−1	koff, s−1	Kd (koff/k′on), nM	P50, mmHg	l′on, μM−1·s−1	loff, s−1	Ld (loff/l′on), nM	M′  Kd/Ld	Autoxidationt1/2, h
HbN wild type	25	0.199	—	0.013	6.75	0.0051	—	7.44	537
HbN Y33L (B10)	—	45	—	—	—	—	—	—	—
HbN Y33F(B10)	—	30	—	—	—	—	—	—	—
C. eugametos wild type*	†	0.0141	—	—	†	0.0022	—	5.0	169
C. eugametos Y63L (B10)*	—	0.95	—	—	—	—	—	—	7.1
N. commune GibN‡	390	79	208	0.55	41	0.01	0.24	867	3.5
Barley Hb§	7.1	0.0272	3.82	—	0.57	0.0011	1.93	2.0	—
Ascaris Hb¶	1.5	0.0041	2.7	0.0038	17	0.018	1.1	2.5	—
Soybean leghemoglobin**	120	5.6	48	0.04	13	0.0078	0.62	78	3.5
Sperm whale Mb‡‡	14	12	857	0.51	0.51	0.019	37	23	13.8

Kinetic constants for HbN represent the overall reactions and are not assigned to the binding or dissociation of the first or the second ligand molecule. l, analogous to k, is the rate constant for carbon monoxide. M′ for HbN, Chlamydomonas, and barley hemoglobins is expressed in molar terms, M′ = 1.34 × M, where M is the experimentally determined value expressed in terms of gas pressures. M′ for other proteins is given by the ratio K_d/L_d. 

^*Couture et al. (28), data obtained at pH 9.5. 

^†Combination rates of five-coordinate Chlamydomonas Hb with ligands are rate limited by the conversion of a six-coordinate species to a five-coordinate species prior to ligand binding (see details in ref. 28). 

^‡Thorsteinsson et al. (14). 

^§Duff et al. (35), k′_on is estimated from M′, k_off, and L_d. 

^‖Gibson and Smith 1965 (36); Antonini and Brunori, 1971 (37). 

^**Gibson et al. (38); Appleby (39). 

^‡‡Springer et al. (40); Antonini and Brunori (37); Brantley et al. (41).