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Control Mechanisms in Hemoglobin Synthesis¹

Division of Biochemistry, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts

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 and ß 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 chains are assembled at a rate much less than that for either and ß chains of hemoglobin A or 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 chains for both hemoglobins A and A₂ proceeds at about the same rate, suggesting a common pool of chains for the 2 hemoglobin types and their synthesis in the same cell.

¹ This work was supported by Grant GB-1687 from the National Science Foundation.

² Present address: The Johns Hopkins Medical School, Baltimore, Maryland.