Table 3.

Subunit assignments for the rate and equilibrium constants for the ‘R state' and rate constants for ‘T-state' of CO binding to MP4 and Hb

Hb	Subunit	k′R (μM−1 s−1)	kR (s−1)	KR (μM−1)	Overall KR (μM−1)	k′T (μM−1 s−1)
Hb	α	2.9	0.019±0.001	152	268	0.23±0.01
	β	9.0		474
MP4	α	4.1	0.022±0.001	186	264	0.38±0.04
	β	12.0	0.032±0.003	375		4.44±1.57

Subunit assignments were based on the fast and slow rates from Table 1, which were assigned to β and α subunits, respectively. ‘R-state' dissociation rates are reported from the NO ligand displacement reactions in Table 1. The equilibrium constants for CO binding to the subunits with ‘R-state' Hbs were calculated from the ratio of the rate constants, K_R=k′_R k_R⁻¹. Overall K_R was calculated as K_R=(K_Rα × K_Rβ)^1/2, according to Equation (4).