Hemoglobin synthesis in beta-thalassemia: the properties of the free alpha-chains.

The decrease in hemoglobin A (HbA, alpha(2)beta(2)) synthesis in the erythroid cells of patients with beta-thalassemia is due to a selective defect in beta-chain synthesis. Since alpha-chains continue to be formed at a normal rate in these cells, this results in a marked relative excess of alpha-chain synthesis over beta- and gamma-chain synthesis. The alpha-chains uncombined with beta- or beta-like-chains (delta, gamma) will be referred to as free alpha-chains. The experiments presented in this paper show that these free alpha-chains are capable of combining with beta-chains to form HbA and are, therefore, structurally normal. Alternatively, in the absence of added beta-chains, alpha-chains aggregates of various sizes are formed. Peripheral blood from patients with beta-thalassemia was incubated with radioactive amino acids and hemolysates were prepared. Column chromatography demonstrates that a majority of the free alpha-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 (Hbbeta(4)) is added to the fresh hemolysates, the free alpha-chains are readily recovered in the HbA peak. This indicates that the free alpha-chains are able to combine normally with beta-chains to form HbA. Freshly labeled hemolysates were also subjected to Sephadex G-100 chromatography. The free alpha-chains eluted as a broad peak migrating between myoglobin and hemoglobin, consistent with their forming alpha-chain aggregates of various mol wt between 16,000 and 64,000. It is suggested that the chromatographic behavior of the free alpha-chains reported herein simply reflects the chemical properties of normal alpha-chains in the absence of adequate numbers of beta- or gamma-chains. The tendency of these free alpha-chains to aggregate may lead to their intracellular precipitation and the subsequent destruction of the cells containing them.