Isolation of high oxygen affinity hemoglobins

Hemoglobin Milledgeville (alpha 44 (CD2) Pro leads to Leu): a new variant with increased oxygen affinity

Hemoglobin Milledgeville, a new hemoglobin structural variant, was identified in three members of a black American family. The oxygen affinity of blood and hemoglobin samples from the affected individuals was markedly increased (p50 O2 of whole blood 11-15 mmHg at 37 degrees C, pH 7.4), and the abnormality was associated with mild erythrocytosis. The variant hemoglobin did not separate from Hb A by electrophoresis or by chromatography or isoelectric focusing, and efforts to isolate an abnormal globin chain were also unsuccessful. The Hb A2 fraction as well as Hb A from erythrocytes of affected individuals exhibited increased oxygen affinity, indicating that the altered oxygen equilibrium was the result of a hemoglobin alpha chain abnormality. Fractionation of trypsin and chymotrypsin digests of isolated alpha chains demonstrated a single abnormal peptide representing a Pro leads to Leu substitution at alpha 44 (CD2). Properties of Hb Milledgeville include low cooperativity (n = 1.1-1.4), a normal alkaline Bohr effect (delta logp50/delta pH = -0.62), and normal interaction with 2,3-diphosphoglycerate. The alpha CD2 proline residue normally participates in the formation of the alpha 1 beta 2 subunit interface in the deoxy quaternary conformation, but not in oxyhemoglobin; the leucine substitution may produce destabilization of the deoxy conformation with a resulting shift in equilibrium toward the oxy conformation.

Familial relative polycythaemia due to haemoglobin Heathrow

Eleven affected members of a New Zealand family carrying the high oxygen affinity haemoglobin Heathrow are described. The detection of high oxygen affinity abnormal haemoglobins may be difficult as haemoglobin and red cell mass may both fall within the normal range and no abnormality may be detected on haemoglobin electrophoresis or by haemoglobin stability tests. The importance of oxygen affinity studies to establish the diagnosis is emphasized.