Table 1.

Comparison of kinetic parameters for multiple-turnover ligation by human DNA ligases

Multiple-turnover parameters were obtained at 150 and 300 mm ionic strength. The ATP dependence was determined with 20 mm fixed concentration of Mg²⁺, and the Mg²⁺ dependence was determined with 1 mm fixed concentration of ATP.

	LIG3α	LIG3β	LIG1a	Relative LIG3α/LIG3β	Relative LIG1/LIG3β
150 mm I
kcat, ATP (s−1)	0.57 ± 0.02	0.55 ± 0.02	0.74 ± 0.09	1.0	1.3
kcat, Mg (s−1)	0.69 ± 0.04	0.69 ± 0.03	0.81 ± 0.10	1.0	1.2
Km, ATP (μm)	34 ± 4	31 ± 3	11 ± 3	1.1	0.35
KMg (mm)	5.6 ± 0.9	7.4 ± 0.7	0.71 ± 0.2	0.76	0.10
kcat/Km, ATP (m−1 s−1)	1.7 ± 0.2 × 104	1.8 ± 0.2 × 104	6.7 × 104	0.94	3.7
kcat/KMg (m−1 s−1)	120 ± 20	93 ± 10	1.1 ± 0.4 × 103	1.3	12
300 mm I
kcat, DNA (s−1)	0.52 ± 0.02	0.51 ± 0.03	0.87 ± 0.10	1.0	1.7
Km, DNA (nm)	62 ± 6	49 ± 8	570 ± 170	1.3	12
kcat/Km, DNA (m−1 s−1)	8.4 ± 0.9 × 106	1.0 ± 0.2 × 107	1.5 ± 0.5 × 106	0.84	0.15

^a The LIG1 values at 150 mm NaCl were previously published (34). The error is represented as S.D. from the mean (n ≥ 3).