Hemoglobin synthesis in β-thalassemia: the properties of the free α-chains

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Abstract
The decrease in hemoglobin A (HbA, α2β2) synthesis in the erythroid cells of patients with β-thalassemia is due to a selective defect in β-chain synthesis. Since α-chains continue to be formed at a normal rate in these cells, this results in a marked relative excess of α-chain synthesis over β- and γ-chain synthesis. The α-chains uncombined with β- or β-like-chains (δ, γ) will be referred to as free α-chains. The experiments presented in this paper show that these free α-chains are capable of combining with β-chains to form HbA and are, therefore, structurally normal. Alternatively, in the absence of added β-chains, α-chains aggregates of various sizes are formed. Peripheral blood from patients with β-thalassemia was incubated with radioactive amino acids and hemolysates were prepared. Column chromatography demonstrates that a majority of the free α-chains are not present in HbA. They are strongly bound to carboxymethylcellulose resin at pHs from 7.0 to 10.0, and do not elute with HbA. However, when chemically prepared hemoglobin H (Hbβ4) is added to the fresh hemolysates, the free α-chains are readily recovered in the HbA peak. This indicates that the free α-chains are able to combine normally with β-chains to form HbA. Freshly labeled hemolysates were also subjected to Sephadex G-100 chromatography. The free α-chains eluted as a broad peak migrating between myoglobin and hemoglobin, consistent with their forming α-chain aggregates of various mol wt between 16,000 and 64,000. It is suggested that the chromatographic behavior of the free α-chains reported herein simply reflects the chemical properties of normal α-chains in the absence of adequate numbers of β- or γ-chains. The tendency of these free α-chains to aggregate may lead to their intracellular precipitation and the subsequent destruction of the cells containing them.