The proportions of G gamma- and A gamma-globins in the fetal hemoglobin synthesized in preterm and term infants.

The change in G gamma to A gamma ratio in relation to the switchover of fetal HB (HbF) to adult Hb (alpha 2 beta 2) synthesis has not been well defined. The gamma-globins of HbF (alpha 2 gamma 2) have either glycine (G gamma) or alanine (A gamma) at position 136. During fetal life the G gamma makes up 70% of the gamma-globins, although they are 40% of the small amounts of HbF in the adult. To further the understanding of this switchover, globin chain synthesis was determined sequentially in eight preterm and 20 full-term infants postnatally. To complete the study, single analysis was also carried out in eight term infants at birth and six preterm infants at the postconceptional age equivalent to term. Blood samples were incubated in an amino acid mixture containing 3H-leucine and subjected to reversed-phase liquid chromatography. The results demonstrated that the fetal proportions of G gamma to A gamma are rigidly controlled according to postconceptional age and not affected by postnatal age after preterm birth. During the early postconceptional age switchover from HbF to adult Hb synthesis, an equal repression of the G gamma and A gamma chains was found. However, based on the values obtained from the term infants, after a postconceptional age of 44 wk, the levels of G gamma to total gamma synthesis begin to decrease and become more variable.