Oxygen affinity and stability of hemoglobin Dunn alpha 6(A4)Asp replaced by Asn): use of isoelectric focusing in recognition of a new abnormal hemoglobin.

A new slow-moving hemoglobin was found in low proportion in an asymptomatic black woman. Isoelectric focusing helped to distinguish it from other hemoglobins with similar electrophoretic mobility, and amino acid analysis showed that aspartic acid alpha 6 (A4) had been replaced by asparagine. Oxygen affinity was increased, but the Bohr and DPG effects were normal. Stability of the purified hemoglobin was decreased, but that of hemolysates was normal. Abnormal oxygen affinity of this variant, and that of hemoglobin Sawara (alpha 6(A4)Asp replaced by Ala), may reflect loss of a salt bridge between Asp alpha 6 and Lys-alpha 127(H10) which would tend to favor the high-affinity R conformation of the molecule.