Table 1.
Binding constants of metal-loaded transferrin and its soluble receptor 1 obtained by HPLC measurement in NH4HCO3 buffer at pH 7.4.
| Metal ion in MxTf | Kd1 (nM)a | Kd2 (nM)a | Log K1b | Log K2b | Log β2c |
|---|---|---|---|---|---|
| La3+ | 42 ± 3 | 916 ± 60 | 7.38 ± 0.03 | 6.04 ± 0.03 | 13.42 ± 0.06 |
| Nd3+ | 110 ± 79 | 332 ± 235 | 6.96 ± 0.24 | 6.48 ± 0.23 | 13.44 ± 0.57 |
| Gd3+ | 231 ± 21 | 709 ± 846 | 6.64 ± 0.04 | 6.15 ± 0.34 | 12.79 ± 0.38 |
| Yb3+ | 267 ± 59 | 1119 ± 69 | 6.57 ± 0.09 | 5.95 ± 0.03 | 12.52 ± 0.12 |
| Lu3+ | 98 ± 1 | 588 ± 221 | 7.01 ± 0.01 | 6.23 ± 0.14 | 13.24 ± 0.15 |
| Th4+ | 65 ± 29 | 250 ± 89 | 7.19 ± 0.16 | 6.60 ± 0.13 | 13.79 ± 0.29 |
| UO22+ | 49 ± 16 | 140 ± 15 | 7.31 ± 0.13 | 6.86 ± 0.04 | 14.17 ± 0.17 |
| Cm3+ | 74 ± 26d | 153 ± 77d | 7.13 ± 0.13 | 6.82 ± 0.18 | 13.95 ± 0.31 |
| Pu4+ | 282 ± 112 | 1766 ± 281 | 6.55 ± 0.14 | 5.75 ± 0.06 | 12.30 ± 0.20 |
| FeCCmNTf | 42d, e | 32d, e | 7.38 | 7.49 | 14.87 |
| Fe3+ | 5.1 ± 1 | 20 ± 5 | 8.30 ± 0.06 | 7.69 ± 0.09 | 15.99 ± 0.15 |
| apoTf | 130 ± 2 | 439 ± 383 | 6.89 ± 0.01 | 6.36 ± 0.27 | 13.25 ± 0.28 |
| Ga3+ | 91 ± 12 | 800 ± 532 | 7.04 ± 0.05 | 6.10 ± 0.22 | 13.14 ± 0.27 |
a
Uncertainties on Kd values are calculated from two independent titrations and two independent data treatments.
b
LogKx is the stepwise binding constant derived from Kdx as follows: Kx = 1/Kdx; uncertainties on log Kx values are calculated by error propagation.
c
Log β2 is the overall binding constant and is calculated as follows: β2= K1 × K2.
d
Previously reported.
e
Value based on a single experimental titration.