Hemoglobin Sendagi (β42 Phe↠Val): A New Unstable Hemoglobin Variant Having an Amino Acid Substitution at Cd1 of the β-Chain

Abstract

Hb Sendsgi, a new unstable hemoglobin variant, was found in a Japanese male and his daughter, who have a moderate hemolytic anemia. The variant showed decreased stability upon heat and isopropanol precipitation tests. The variant did not separate from hemoglobin A by electrophoresis, but the abnormal chain emerged ahead of the normal β-chain on reverse-phase HPLC. Structural analyses revealed that the phenylalanine β42 (CD1), one of the critical amino acid residues in the heme pocket, had been replaced by valine. Oxygen equilibrium studies of the patient's hemolysates indicated that Hb Sendagi had a lowered oxygen affinity and a normal response to 2,3-diphosphoglycerate. Hb Hammersmith (β42 Phe→Ser) and Hb Louisville (Bucuresti) (β42 Phe→Leu) have previously been reported to have varying degrees of molecular instability and altered oxygen binding function. Hb Sendagi provides an additional model for elucidation of the role of the phenylalanine βCD1 on the structure and function of hemoglobin.