Polypeptide Chains of Hæmoglobin A ₂

Abstract

HÆMOGLOBIN A ₂ (Hb-A ₂), first described by Kunkel and Wallenius¹, is a minor component found in normal adult hæmolysate which has an electrophoretic mobility slower than Hb-A at alkaline pH. Several variants of Hb-A ₂ have been described and these now fall into two groups. While the minor hæmoglobins of one group can occur when Hb-A is normal, for example, Hb-A′₂ (ref. 2) and Hb-B ₂ (ref. 3), those of the other group are always associated with α-chain variants of Hb-A. Shooter, Skinner, Garlick and Barnicot⁴ described a minor hæmoglobin variant of the latter group which they called Hb-G ₂ in an individual carrying Hb-G _Ibadan. Since the charge relationship between Hb-G ₂ and Hb-G _Ib. was similar to that between Hb-A ₂ and Hb-A, Gammack, Huehns, Shooter and Gerald⁵ suggested that Hb-G ₂ was the naturally occurring hybrid of Hb-A ₂ and Hb-G _Ib. This hypothesis implied not only that Hb-G _Ib. has abnormal α₂ sub-units, but also that Hb-A ₂ differs from Hb-A only in the composition of the non-α₂ sub-unit and has the molecular formula ${\text{α}}_{\text{2}}^A{\text{δ}}_{\text{2}}^{A_{\text{2}}}$. It has already been shown⁵ that Hb-G _Ib. consists of normal β^A ₂ and abnormal ${\text{α}}_{\text{2}}^G$ sub-units, and the results now reported are consistent both with the above formula for Hb-A ₂ and with the suggestion that Hb-G ₂ carries the abnormal sub-unit of Hb-G _Ib. and the specific sub-unit of Hb-A ₂.