Table 1.

Calculated and observed chemical shifts (ppm) for distal and proximal histidines of HbCO A and HbO₂ A

Chem. shift assignment	HbCO A			HbO2 A
	2HCO, ppm	1BBB, ppm	obs., ppm	1HHO, ppm	obs., ppm
α58His Hδ2	4.90	4.83	4.51	4.89	4.83
β63His Hδ2	5.16	4.91	4.58	4.93	4.65
α58His Hɛ1	8.48	8.34	8.23	7.15	5.64
β63His Hɛ1	8.14	8.50	8.38	8.12	6.81
α58His Hɛ2	7.42	5.65	*	5.36	5.42
β63His Hɛ2	5.63	5.62	*	5.26	4.79
α87His Hδ1	10.04	9.46	9.42	9.78	10.73
β92His Hδ1	9.13	9.47	9.34	8.65	10.64
α87His Hδ2	1.25	1.66	1.00	1.42	0.77
β92His Hδ2	1.27	1.70	0.90	0.88	0.40
α87His Hɛ1	1.87	1.41	1.43	1.70	2.77
β92His Hɛ1	1.54	1.85	1.39	1.86	2.74
rms deviation	0.38	0.39	—	0.99	—

Chemical shifts of corresponding protons in the α- and β-subunits are listed in adjacent rows. The last row lists the rms deviation between the observed chemical shifts and those calculated for each structure. 

^*Not observed in HbCO A, because of rapid exchange of the distal histidine Hε₂ with water.