Table 1. Ca²⁺ Affinities and Free Energies of Binding for CaM1 or CaM4 in the Absence and Presence of Mg²⁺.

CaM	Kd,N,ave (μM)a	Kd,C,ave (μM)b	Kd,ave (μM)c	ΔGN (kJ mol−1)	ΔGC (kJ mol−1)	ΔG1,2,3,4 (kJ mol−1)
s-CaM1	36.2 ± 7.4	6.2 ± 0.2	14.9 ± 1.8	−51.8 ± 1.1	−60.4 ± 0.1	−112.2 ± 1.2
+ 10 mM Mg2+	107.8 ± 5.5	14.8 ± 0.6	39.8 ± 0.5	−46.1 ± 0.2	−56.1 ± 0.2	−102.1 ± 0.0
s-CaM4	13.0 ± 0.8	2.0 ± 0.5	5.0 ± 0.8	−56.9 ± 0.7	−66.3 ± 1.2	−123.3 ± 1.8
+ 10 mM Mg2+	29.2 ± 6.6	34.1 ± 6.8	31.5 ± 6.7	−52.8 ± 0.9	−52.0 ± 1.0	−104.9 ± 1.9

From our NMR data, sites 1 and 2 can be assigned to the C-terminal lobe and sites 3 and 4 to the N-terminal lobe.

^aK_d,N,ave = (K₃K₄)^−1/2.

^bK_d,C,ave = (K₁K₂)^−1/2.

^cK_d,ave = (K₁K₂K₃K₄)^−1/4.