Hb Isehara (or Hb Redondo) [beta 92 (F8) His----Asn]: an unstable variant with a proximal histidine substitution at the heme contact.

A 50-year-old Japanese female patient was found to have hemolytic anemia. Isoelectrofocusing of her hemolysate revealed two abnormal hemoglobin bands, one of which was very close to the Hb A2 band, and the other between the Hb A2 and Hb F bands. CM-cellulose column chromatography of the globin prepared from the abnormal hemoglobin showed that the abnormal chain eluted faster than the normal beta and delta chains; the beta X chain, however, did not separate from the normal beta chain in urea cellulose acetate electrophoresis. An instability test of the patient's hemolysate revealed the presence of an unstable component. Structural analysis of the abnormal beta chain indicated that the histidine residue at beta 92(F8) was replaced by an asparagine or aspartic acid residue. DNA amplified by polymerase chain reaction was sequenced by the dideoxy method. The nucleotide sequence of the beta 92 codon was AAC instead of CAC, suggesting that the amino acid substitution corresponded to His----Asn, which is the same as is found in Hb Redondo or beta 92(F8)His----Asn----Asp.