Hemoglobin biosynthesis in individual bursts from human adult peripheral and umbilical cord blood: analysis of the relative rates of synthesis of G gamma and A gamma globin chains.

We cultured human adult peripheral and umbilical cord blood mononuclear cells in methylcellulose and measured the synthetic rates of globin chains in individual erythropoietic bursts. Globin chains were labeled with 14C-amino acids in culture, separated by isoelectric focusing in slab gels containing 8 M urea and 3% Nonidet P-40, and quantitated by fluorographic methods. All bursts exhibited G gamma, A gamma, and beta chains in varying ratios. Cumulative frequency distributions of individual bursts differing in the ratios of G gamma/(G gamma + A gamma) and gamma/(gamma + beta) approached normal distributions. These results indicated that perinatal hemoglobin switching and the hemoglobin switching of cultured adult erythropoietic precursors do not involve population changes in the precursors. Further, a positive correlation between gamma/(gamma + beta) and G gamma/(G gamma + A gamma) ratios of individual bursts existed in all of the samples. Switching between gamma and beta chains and switching of G gamma: A gamma ratios may share common regulatory mechanisms.