The G gamma:A gamma composition of fetal hemoglobin in fetuses and newborns.

To determine whether the G gamma:A gamma HbF switch is coordinated in development with the HbF:HbA switch, hemoglobin F Gly/Ala (G gamma:A gamma) heterogeneity was evaluated by electrophoresis on polyacrylamide gels. The mean G gamma was 70% in 19 newborns, similar to the published value of 73% obtained by amino acid analysis of the gamma CG-3 peptide. In 29 fetuses at 18-20-wk gestation, G gamma was 71%. The values were similar in normal fetuses and newborns and in those with hemoglobinopathies. The synthetic ratio of 3H-leucine-labeled G gamma:A gamma was identical to the ratio found in the globin protein accumulated by 20 wk. The proportion of G gamma was also identical in 6 paired samples, at 20-wk gestation and at birth. Thus, G gamma production does not decline with respect to A gamma in utero at the time of onset of the HbF:HbA switch.