Some properties of hemoglobin A2.

While no significant physiologic function of hemoglobin A2 (Hb A2), the minor basic component of human hemoglobin, has been recognized, only its oxygen equilibria have been studied in detail. Since hemoglobin A2 and its oxidative denaturation product, hemichrome A2, bind to the red cell membrane, particularly to band 3, to a greater extent than do Hb A or hemichrome A, some of the properties of Hb A2 that might influence hemoglobin-membrane association were examined. Hemoglobin A2 exhibited slightly increased susceptibility to autoxidation to methemoglobin. No differences were noted between methemoglobins A and A2, including the rates of enzymatic reduction and stability of the heme-globin linkage. Oxyhemoglobin A2 had a slightly lower solubility in phosphate buffer than did hemoglobin A. While the hemichromes (prepared with phenylhydrazine) of hemoglobins A2 and A had the same optical spectra, the A2 hemichrome exhibited greater stability. It is suggested that the differences in products of oxidative denaturation may provide the basis for functional differences between hemoglobins A2 and A.