Table 1.

Mean K_d (8-N₃ATP) values of wild-type and mutant MRP1

Samples		Kda of NBD1 (μ M 8-N3ATP)	Kd of NBD2 (μ M 8-N3ATP)
N-half	C-half
Wild-type	Wild-type	11.7 ± 2.7	32.4 ± 2.5
H827L	Wild-type	59.5 ± 0.5b	60.0 ± 3.0
Wild-type	H1486L	31.0 ± 0.8	58.7 ± 1.3
H827L	H1486L	59.7 ± 1.3	53.0 ± 0.8
H827F	Wild-type	12.3 ± 0.5	32.7 ± 0.9
Wild-type	H1486F	11.5 ± 0.5	33.0 ± 1.0
H827F	H1486F	58.0 ± 1.0	51.5 ± 0.5

^aThe K_d (8-N3ATP) values (n = 3) of wild-type and mutant MRP1s were derived from Figure 2. The amount of [α -³²P]-8-N₃ATP incorporated into the N-half (NBD1) or C-half (NBD2) fragment was measured by Packard Instant Imager and plotted out against [α -³²P]-8-N₃ATP concentration. K_d is calculated by using the formula: K_d = (L_max–L)[S]/L, where [S] is the concentration of [α -³²P]-8-N₃ATP, L is the amount of [α -³²P]-8-N₃ATP labeled on NBD1 or NBD2 and L_max is the maximum amount of [α -³²P]-8-N₃ATP labeled on NBD1 or NBD2.

^bStatistical analysis indicated that the K_d values of NBD1 from H827L, H1486L, H827L/H1486L and H827F/H1486F or the K_d values of NBD2 from H827L, H1486L, H827L/H1486L and H827F/H1486F are significantly different from that of wild-type NBD1 (11.7 μ M 8-N₃ATP) or wild-type NBD2 (32.4 μ M 8-N₃ATP). In contrast, the K_d values of NBD1 or NBD2 from H827F or H1486F are not significantly different from that of wild-type NBD1 (11.7 μ M 8-N₃ATP) or wild-type NBD2 (32.4 μ M 8-N₃ATP).