The Binding of Cr⁵¹ to Hemoglobin I. In Vitro Studies

By a number of different technics, confirmatory evidence has been obtained that Cr⁵¹ activity of Hb A₁ tagged with Na₂Cr⁵¹O₄ in a ratio of approximately 1 mole chromium to 1000 mole of hemoglobin is largely associated with the β polypeptide chains. No significant difference in the site or strength of chromium binding could be demonstrated in abnormal hemoglobins resulting from point amino acid substitutions (Hbs S and C).

The results obtained with Hb F were very suggestive of γ chain binding, but an apparently weak Hb F-Cr⁵¹ bond or increased elution rate markedly hampered such studies.

The propensity of Cr⁵¹ for preferential tagging of β chains was seen not only when hemoglobin was tagged intact, but also when isolated β chains were tagged. This may indicate that there is a specific locus or chemical configuration within the β chains where Cr⁵¹ tagging occurs. Knowledge of the exact total amino acid sequence of α, β, and γ chains should soon be available and may permit a precise identification of such a Cr⁵¹ binding site.

Whether the results of this type of highly artificial manipulation of hemoglobin has significance in Cr⁵¹ red cell survival studies in clinical situations where large amounts of Hb F occur is uncertain. Conflicting results of red cell survival studies of the fetal red cells suggests that it may.^27,28 Further investigation of this problem is currently in progress.