Chemical studies on haemoglobins A1 and A0

Abstract

The 2 forms of adult human hemoglobin, A1 and A0, have identical amino acid composition, and (in their met, cyanmet or oxy forms) are interconvertible, the conversion being influenced by the concentration of hemoglobin, chloride and cyanide. The attainment, from 1 component, of a mixture containing equal amounts of the 2 forms is facilitated by toluene, freezing and freeze-drying. Methemoglobin A1 requires a large excess of cyanide, as compared with methemoglobin A0, to reach complete cyanide saturation as indicated by a shift of the Soret peak from 409 to 420 m[mu]. Chloride, phosphate and pH play no part in this spectral shift, although they have some influence on the spectra of methemoglobins A1 and A0, and in the case of pH on cyanmethemoglobins A1 and A0. Aggregation or dissociation to sub-units was not responsible for the A1 [image] A0 transformation. The me, cyanmet or oxy forms of hemoglobin A1 have 2 more negative changes than those of hemoglobin A0 and are more easily denatured, Mathemoglobin A0 carries 2 titratable SH groups that react with N-ethylmaleimide, p-hydroxymercuribenzoate and iodoacetamide, whereas methemoglobin A1 has no titratable SH groups. Methemoglobin A0 or oxyhemoglobin A0 has a higher binding capacity for Cr than have the corresponding forms of hemoglobin A1.