TABLE 1.

Ligand binding parameters for CmaHb compared with wild type human Ngb with the disulfide bond (31)

Note that Ngb and DTT (to reduce the cysteines) or the mutant Ngb without cysteines has a 10-fold lower oxygen affinity due mainly to a lower His dissociation rate. On/off-rates were measured at 25 °C in 50 mm Tris/HCl, 150 NaCl, 5 mm DTT, pH 8.5.

	CmaHb	Human Ngb
kon(CO) (μm/s)	40	40
kon(O2) (μm/s)	100	140
koff(O2) (s)	5.8	0.8
K(O2) (nm)	55	5.7
kon(His) (s)	≈100	2000
koff(His) (s)	5	7
KHis	20	280
P50(O2) (Torr)	0.5a	0.9

^a This value is also measured at equilibrium.