Table 1.

Kinetic and equilibrium constant governing binding of BirA variants to biotin and bio-5`-AMP^a

Variant/ ligand	koff (s−1)	kon(M−1 s−1)	KD(M)
biotin
wt	0.33 (±0.01)	7.4 (±0.3) × 106	4.5 (±0.2) × 10−8
G115S	80 (±20)	9 (±2) × 106	9 (±3) × 10−6
R118G	29 (±5)	1.6 (±0.2) × 107	1.8 (±0.4) × 10−6
R119W	0.49 (±0.04)	2.2 (±0.2) × 106	2.5 (±0.3) × 10−7
bio-5`-AMP
wt	0.00027 (±0.00003)	6.0 (±0.6) × 106	4.5 (±0.7) × 10−11
G115S	0.84 (±0.03)	7.0 (±0.7) × 106	1.2 (±0.1) × 10−7
R118G	0.119 (±0.006)	6 (±1) × 106	2.0 (±0.3) × 10−8
R119W	0.00009 (±0.00001)	4.9 (±0.2) × 106	1.8 (±0.2) × 10−11

^a All parameters were previously reported in Kwon and Beckett (2000). The equilibrium dissociation constants (K_D) were calculated from the measured unimolecular dissociation rate constants (k_off) and bimolecular association rate constants (k_on) using the equation . Parameters were determined in Standard Buffer (10 mM TrisHCl, pH 7.50 ± 0.02, 200 mM KCl, 2.5 mM MgCl₂ at 20.0 ± 0.1°C).