TABLE 1.

Steady-state kinetic parameters for HPG activation by equimolar complexes of SK or the various 170 loop mutants and HPN

The kinetic parameters for substrate HPG activation were determined at 22 °C with the chromogenic substrate in 50 mm Tris-Cl buffer, pH 7.5, 100 mm NaCl as described under “Experimental Procedures.” The data represent the mean of three independent determinations.

Activator species	Km	kcat	kcat/Km
	μm	min−1	min−1μm−1
wtSK	0.40 ± 0.05	7.50 ± 0.3	19.00
P171A	0.40 ± 0.04	7.00 ± 0.5	17.50
D172A	0.50 ± 0.06	7.00 ± 0.5	14.0
D173A	0.50 ± 0.08	7.10 ± 0.4	14.2
D174A	0.50 ± 0.07	6.50 ± 0.3	13.0
R176A	0.60 ± 0.06	4.50 ± 0.4	7.5
P177A	0.45 ± 0.08	0.80 ± 0.03	1.7
K180A	0.50 ± 0.03	0.70 ± 0.01	1.40
D181A	0.55 ± 0.06	3.50 ± 0.34	6.3
K180D	0.50 ± 0.06	0.20 ± 0.06	0.4
K180G	0.60 ± 0.05	0.60 ± 0.04	1.0
K180R	0.50 ± 0.07	3.20 ± 0.50	6.4
177 pro del	0.60 ± 0.05	0.80 ± 0.06	1.3
R176A/K180A	0.60 ± 0.08	0.70 ± 0.15	1.2
R176A/D181A	0.40 ± 0.07	4.00 ± 0.45	10
P177A/K180A	0.50 ± 0.07	0.70 ± 0.02	1.4
K180A/D181A	0.50 ± 0.06	0.80 ± 0.03	1.4
R176A/K180A/D181A	0.60 ± 0.08	0.40 ± 0.04	0.6