TABLE 2.

Kinetic parameters for activation of three CBS-PPases by diadenosine polyphosphates with n = 4–6 in the presence of 5 mm Mg²⁺

The value of the Hill coefficient was indistinguishable from unity in all cases.

Enzyme/dinucleotide	[MgPPi]	vN/v0a	KNb
	μm		nm
dhPPase
Ap4A	1	18 ± 1	12.1 ± 0.3
	50	3.0 ± 0.1	4.9 ± 0.2
	300	1.91 ± 0.02	4.3 ± 0.2
Ap5A	50	3.32 ± 0.06	5.5 ± 0.2
Ap6A	50	2.58 ± 0.06	4.4 ± 0.3
cnPPase
Ap4A	1	6.0 ± 0.3	3.9 ± 0.1
	50	3.14 ± 0.05	7.0 ± 0.2
	300	1.51 ± 0.01	16.5 ± 0.7
Ap5A	50	3.03 ± 0.08	4.9 ± 0.3
Ap6A	50	2.08 ± 0.03	3.3 ± 0.2
cpPPase
Ap4A	1	14.7 ± 0.4	293 ± 5
	50	2.52 ± 0.03	62 ± 2
	300	2.04 ± 0.02	33 ± 1
Ap5A	50	2.30 ± 0.03	58 ± 2
Ap6A	50	2.04 ± 0.02	187 ± 9

^a v_N and v₀ are activities extrapolated to infinite concentration of the variable nucleotide and measured in the absence of any nucleotide, respectively.

^bThis parameter is equivalent to $\sqrt{K_{\text{N}1}{K}_{\text{N}2}}$ in Table 1.