TABLE 3.
Comparison of apparent rate and equilibrium constants for hemin binding to apoIsdA, apoIsdC, and other hemin protein complexes
| Heme protein | k′hemin μM−1 s−1 | k-hemin s−1 | Khemin M−1 | Reference |
|---|---|---|---|---|
| apoIsdA | ||||
| Without apoIsdC | 100 | 0.00026 | 3.8 × 1011 | This work |
| With apoIsdC | 54.3 | |||
| apoIsdC | ~3.8 × 1012a | This work | ||
|
| ||||
| ApoShp | 14 | |||
| without apoHtsA | 1.6 | 0.0003 | 5 × 109 | |
| with apoHtsA | 43 | |||
| ApoHtsA | 80 | 0.0026 | 3.1 × 1010 | 14 |
|
| ||||
| Hemophore HasA | 5.3 × 1010 | 31 | ||
|
| ||||
| Human apohemoglobin | 33 | |||
| α (tetramers) | ~100 | 0.00008 | ~1.2 × 1012 | |
| α (dimers) | ~100 | 0.00016 | ~6 × 1011 | |
| α (monomers) | ~100 | 0.0033 | ~3.3 × 1010 | |
| β (tetramers) | ~100 | 0.00041 | ~2.5 × 1011 | |
| β (dimers) | ~100 | 0.0042 | ~2.4 × 1010 | |
| β (monomers) | ~100 | 0.011 | ~9 × 109 | |
a
Estimated from the value of Khemin of IsdA and the equilibrium constant (Keq = 10) of the reaction of holoIsdA with apoIsdC on the assumption that the Keq value is solely dependent on the relative affinity of IsdA and IsdC for hemin.