TABLE 2.

K_m constants for binding of effectors by mouse and human SAMHD1

The experiments measured binding of increasing concentrations of effectors to site 2 in the presence of a fixed concentration of substrate and of GTP (binding to site 1). Effector K_m values are the mean ± S.E. from three or more identical experiments or from a single experiment (indicated by *) for which the indicated variability is the S.E. of the curve fitting.

Mouse SAMHD1					Human SAMHD1
Effector	GTP	Substrate	Km		Effector	GTP	Substrate	Km
			Site 1	Site 2				Site 1	Site 2
	μm		μm	μm		μm		μm	μm
GTP		dATP	0.5 ± 0.1		GTP		dATP	0.15 ± 0.01*
dGTP			0.8 ± 0.1		dGTP			0.14 ± 0.03*
dATP	20	dTTP		2.5 ± 0.4	GTP		dTTP	0.10 ± 0.01*
	500			1.5 ± 0.1
dATP	20	dCTP		11 ± 1.3	dATP	20	dCTP		1.2 ± 0.2
	500			8 ± 1		500			0.9 ± 0.4*
dTTP	20	dCTP		50 ± 1.2	dTTP	20	dCTP		2.1 ± 0.6