TABLE 4.

Thermodynamic parameters of APS binding to the AtAPSK·SO₄²⁻ complex, G111A, and G113A proteins

All titrations were performed at 17 °C as described under “Experimental Procedures.” ITC data were fit to either a one-site binding model (n = number of sites) or a two-site binding model.

Protein	Titrant	K1	K2	ΔH1	ΔH2
		μm		kcal mol−1
AtAPSK·SO42−	APS	3.78 ± 2.55 n = 1.98 ± 0.04		−8.0 ± 0.6
AtAPSK G111A	APS	102.7 ± 30.1	439.0 ± 131.8	−6.4 ± 2.2	−2.7 ± 1.9
AtAPSK G113A	APS	130.0 ± 45.6	365.9 ± 93.7	−9.1 ± 4.6	−5.4 ± 2.5