Gγ and Aγ Globin-Chain Biosynthesis by Adult and Umbilical Cord Blood Erythropoietic Bursts and Reticulocytes

We examined γ-globin-chain biosynthesis by adult and umbilical cord blood erythropoietic bursts in methylcellulose clonal culture and γ-chain synthesis by cord blood reticulocytes. Globin chains were labeled with 14C-amino acids and quantitated by using autoradiography or fluorography. Alpha, beta, and Gγ and Aγ chains were separated by isoelectric focusing in polyacrylamide gels containing 8 M urea and 3% Nonidet P-40 (a nonionic detergent). Time course examinations of the γ-chains synthesized by the bursts revealed no changes in the Gγ:Aγ ratio between days 10 and 18 of culture. The ratio of Gγ/(Gγ + Aγ) in cultures of adult circulating erythroid precursors was 0.38 ± 0.09, which corresponds to the known ratio in adult peripheral blood erythrocytes. The relative G7-chain biosyntheses in the cord blood bursts and reticulocytes were 0.56 ± 0.02 and 0.66 ± .008, respectively. Both are intermediate between the accepted newborn and adult ratios. Natal erythropoietic precursors appear to be in the transitional stage with respect to the switching of Gγ:Aγ ratios.