TABLE 2.

Effects of various nucleotides on transport activities of His₁₀-Npt1_Ct and His₁₀-Npt2_Ct

Effector	Rate of nucleotide transport (%)a
	ATP import His10-Npt1Ct	GTP import His10-Npt2Ct
None	100.0	100.0
dATP	96.5	100.7
dGTP	100.6	92.6
dCTP	106.4	97.0
dTTP	108.7	94.7
AMP	100.5	NM
GMP	NM	90.5
ADP	12.0	NM
GDP	NM	89.1
Guanosine tetraphosphate	NM	97.1

^aATP uptake was measured at a substrate concentration of 100 μM; GTP uptake was measured at a substrate concentration of 50 μM. The effectors were always present in a 2.5-fold-higher concentration than the substrates. ATP uptake by His₁₀-Npt1_Ct in the absence of effectors was 251.9 nmol · mg of protein⁻¹ · h⁻¹; GTP uptake by His₁₀-Npt2_Ct in the absence of effectors was 75.7 nmol · mg of protein⁻¹ · h⁻¹. NM, not measured. Data are means of three independent experiments.