Molecular models of the central cavity between the two δ-globin chains of (A) coast and (B) eastern mole hemoglobins. In coast mole deoxyhemoglobin, this cavity is lined by 8 cationic residues (δ1Val, δ2His, δ82Lys and δ143His) that form competitive binding sites for anions (Cl-, lactate and DPG) that stabilize the low O2 affinity T-state conformation. In eastern mole deoxyhemoglobin, the carboxylate side chain of δ136Glu forms a salt bridge with ε-amino group of δ82Lys of the same chain, thus deleting key docking sites for these anions, and reducing competition for CO2 binding (carbamate formation) at the N-terminus (δ1Val). This change is expected to markedly increase the maximal CO2 carrying capacity of eastern mole blood.
Campbell et al. BMC Evolutionary Biology 2010 10:214 doi:10.1186/1471-2148-10-214