Table 2.

Comparison of fish Hb quaternary structures

Structures	Root-mean-square deviations, Å*			α1β1/α2β2 rotation angle, °†
	α1β1 dimer	α2β2 dimer‡	Tetramer
HbTbCO vs. HbTb-deoxy	0.37	4.80 (0.40)§	1.59	11.5
HbTbCO vs. HbTn[α(CO)β(hemi)]2	0.39	1.97 (0.37)§	0.68	4.6
HbTn[α(CO)β(hemi)]2 vs. HbTb-deoxy	0.32	3.06 (0.36)§	1.08	7.5
HbTnCO vs. HbTn[α(CO)β(hemi)]2	0.37	1.98 (0.37)§	0.71	4.8
HbTnCO vs. HbTbCO	0.21	0.47 (0.21)§	0.25	1.6
HbTn[α(CO)β(hemi)]2 vs. R2Hb¶	0.77	5.54 (0.74)§	1.75	17.2

^*The N, C^α, C atoms of the BGH core were used for the superimpositions. 

^† The α₁β₁/α₂β₂ rotation angle is the angle required to superimpose the α₂β₂ dimer after the fitting of the α₁β₁ dimer. 

^‡ These values correspond to the root-mean-square deviations of the α₂β₂ dimers after the fitting of the α₁β₁ dimers. 

^§ The value given in parenthesis corresponds to the root-mean-square deviations of the α₂β₂ dimers after their superimposition. 

^¶ This notation identifies the fully liganded R2 state of human Hb.