Peptide Chain Synthesis of Human Hemoglobins A and A2

Abstract

Abstract Human bone marrow was pulse-labeled with radioactive amino acids for various times. Hemoglobin A after 3 min of pulse showed a sudden increase in the relative specific activities of peptides between position 90 and the COOH terminus in both the α and β chains. A control point in this region is postulated beyond which the growth of the polypeptide chains is markedly reduced, perhaps because of the assumption of a specific tertiary conformation of the growing chains after heme insertion. Pulse labeling of hemoglobin A2 indicates that δ chains are assembled at a rate much less than that for either α and β chains of hemoglobin A or α chains of hemoglobin A2. This can, in part, account for the small quantity of hemoglobin A2 with respect to hemoglobin A found in normal peripheral blood. Also, as cells age, their capacity to produce hemoglobin A2 is lost at a greater rate than their capacity to produce hemoglobin A. The assembly of α chains for both hemoglobins A and A2 proceeds at about the same rate, suggesting a common pool of α chains for the two hemoglobin types and their synthesis in the same cell.