Table 2. On and Off Rates and Binding Constants for Several Protein-NO (or CO) Complexes.

	kon(M–1 s–1)	koff (s–1)	KCat-NO = kon/koff (M–1)
Mb(Fe2+)COa	5.1 × 105	1.9 × 10–2	2.7 × 107
Mb(Fe2+)NOa	1.7 × 107	1.2 × 10–4	1.4 × 1011
Mb(Fe3+)NOb	4.8 × 104	42	1.14 × 103
Lb(Fe2+)NOa	1.2 × 108	2.0 × 10–5	5.9 × 1012
NP1(Fe3+)NOc	1.5 × 106 (pH 5)	0.18 (pH 5)	8.3 × 106 (pH 5)
	1.5 × 106 (pH 8)	1.25 (pH 8)	1.2 × 106 (pH 8)
NP4(Fe3+)NOc	2.1 × 106 (pH 5)	0.11 (pH 5)	2.0 × 107 (pH 5)
	2.3 × 106 (pH 8)	1.24 (pH 8)	1.9 × 106 (pH 8)
Cat(Fe3+)NOd	1.3 × 107	1.5	8.7 × 106

^aFrom ref (60). Lb is leghemoglobin.

^bFrom ref (67).

^cFrom ref (64). The nitrophorins adopt closed and open conformations at pH 5 and 8, respectively.

^dFrom this work.