Table 1.

Kinetic parameters for MbCO and isolated HbCO α and β chains.^a

Variant	kFeCO (μs−1)	kinCO[CO]c (μs−1)	koutCO (μs−1)	kinH2O[H2O] (μs−1)	koutH2O (μs−1)	nw	X-ray Structure H2O Occupancy	φg	1− nw	k′[CO]e (μs−1)	τobs−1 (μs−1)
Mbb	0.11	(0.08)	2.2	9.0	1.7	0.84	0.84	0.051	0.16	0.00064	0.00066
α Native f	3.4	(0.08)	21	6.0g	3.4	0.64	1.00d	0.14	0.36	0.0040	0.0057
β Native f	1.6	(0.08)	6.0	6.0	20	0.23	0.00d	0.22	0.77	0.014	0.011

^aRate constants and inverse lifetimes reported in μs⁻¹; [CO] = 1.0 mM; [H₂O] = 55.5 M.

^bKinetic parameters from Goldbeck et al,¹² crystal structure water occupancy from Quillin et al.¹⁵

^cConstrained during fitting procedure to a maximum (diffusion controlled) value of 0.08 μs⁻¹.

^dWater occupancy values from high resolution crystal structure of deoxyHb tetramer.⁴¹

^ek′ ≡ (1 − n_w)φ_gk_in^CO.

^fThe φ_g values of the chains were fixed at the value measured by Birukou et al., as were k_Fe^CO and k_out^CO.²⁴

^gThe α chain value for k_in^H₂O[H₂O] was fixed at the value obtained for the β chains.