Further studies on the isolation and properties of alpha-chain sub-units of haemoglobin

1. α^A-Chain sub-units have been isolated from neutral haemolysates containing certain unstable β-chain haemoglobin variants. They are identical, in electrophoretic properties, tryptic peptide analyses and their ability to recombine with Hb-β^A₄ at neutral pH, with the α^A-chain sub-units isolated from Hb-A at acid pH. Abnormal α^G-chain sub-units have been prepared from haemolysates containing the α-chain variant Hb-G. 2. α^A-Chain sub-units prepared by either method are eluted from Sephadex at low haemoglobin concentration as monomer sub-units. The elution volume, sedimentation coefficient and apparent molecular weight are, however, concentration-dependent, suggesting an equilibrium between monomers and higher polymers with the former as the predominant species. Elevated temperatures cause the α^A-chain sub-unit to aggregate and denature. 3. The product of the reaction between the α^A-chain sub-unit and Hb-β^A₄ has been characterized as Hb-A. Only Hb-A and Hb-G can be detected as the products when a mixture of α^A- and α^G-chain sub-units reacts with Hb-β^A₄. The absence of the species α^Aα^Gβ^A₂ can be explained in terms of the rapid equilibrium between whole and half haemoglobin molecules and the reassortment of αβ sub-units during the separation process.