Table 1.
Structural parameters of the α and β subunits
| α1 | α2 | β1 | β2 | Reference | |
|---|---|---|---|---|---|
| Number of amino acid residues | 141* | 146* | (Perutz 1970) | ||
| Number of α-helices | 7 | 8 | (Perutz 1970) | ||
| Fe-His bond distance in deoxyHbA/Å | 2.20 | 2.21 | 2.16 | 2.19 | (Park et al. 2006) |
| Fe-His bond distance in oxyHbA/Å | 2.07 | 2.06 | (Park et al. 2006) | ||
| H-bond distance from Nε2 of His H7/Å | (Park et al. 2006) | ||||
| O1, | 2.82 | 3.06 | |||
| O2: | 2.70 | 3.02 | |||
| Fe–O-O angle (°) | 124 | 126 | (Park et al. 2006) | ||
| Fe-His stretching frequency in deoxyHb/cm−1 | (Nagai and Kitagawa 1980) | ||||
| T-state | 203–207 | 217–220 | |||
| R-state | 222–223 | 224 | |||
| O2 binding kinetic constant, k’on/μM−1 s−1 | (Unzai et al. 1998) | ||||
| T-state | 11 | 4.0–5.8 | |||
| R-state | 36–40 | 77–80 | |||
| O2 dissociation kinetic constant, koff/s−1 | (Unzai et al. 1998) | ||||
| T-state | 4300–5200 | 1300–2100 | |||
| R-state | 12–14 | 25–31 | |||
| K = koff/k’on | (Unzai et al. 1998) | ||||
| T-state | 0.0021–0.0026 | 0.0019–0.0045 | |||
| R-state | 2.9–3.0 | 2.6–3.1 | |||
| Effect of O2-binding on quaternary structure | Large | Small | (Nagatomo et al 2011a) | ||
| Role of Fe-His bond in O2-affinity control | Essential to T → R structure change | Lowering of affinity of α subunit | (Nagatomo et al. 2015) | ||
* When the number is present between α1 and α2 columns or between β1 and β2 columns, it means that α1 and α2 (or β1 and β2) cannot be distinguishable. When two numbers are combined with a hyphen, a precise number cannot be determined but is located between the two numbers