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Iron incorporation (59Fe) into erythropoietic cells from adult and foetal (11- to 15-day) peripheral blood and from foetal (12- to 15-day) livers has been investigated. Ion-exchange chromatography of haemolysates from such cells revealed two groups of 59Fe-containing proteins. The first group (X-fraction) was eluted from CMC-columns in the void volume and was highest in lysates of immature erythropoietic cells. This fraction contained a radiolabelled haemprotein of high molecular weight as well as other 59Fe-containing proteins. The haemprotein does not appear to be related to haemoglobin. The second group consisted of haemoglobins. One major (A1) and two minor (A2 and A3) haemoglobins were found in adult peripheral blood. In foetal liver lysates two major (F1 and A1) and two minor (F2 and A3) haemoglobins were present. The relative proportion of the major haemoglobins changed during development. Haemoglobin F1 was highest in the more mature livers. F1 proved to be different from A1 by chromatographic behaviour, in polypeptide chain composition and in fingerprints. A unique foetal polypeptide chain, intermediate in electrophoretic behaviour between the adult α- and β-chain, was identified. In young foetal peripheral blood (11-day), in which 95% of the cells are of yolk-sac origin, one major (E1), two intermediate (E2 and E3) and one minor (F1) haemoglobin were demonstrable. Haemolysates of the peripheral blood of older embryos contain haemoglobins from erythroid cells of both yolk-sac and foetal liver origin. The haemoglobin pattern of such lysates is explicable in terms of the decreasing amount of embryonic haemoglobins (E1, E2 and E3) and the increasing amount of foetal haemoglobins (F1 and A1). Since A1 and E1 are the most prominent haemoglobins of livers from young embryos and yolk-sac erythrocytes respectively, and since they are very similar in chromatographic behaviour, foetal peripheral blood at all stages contains one dominant haemoglobin peak in the A1-E1 region. Most authors have neglected the relatively slight elevation of the foetal haemoglobin peak (F1) in front of A1-E1, the more because the F1-A1 region has been suspected sometimes to contain artificial haemoglobin components (Riggs, 1965). This probably explains why no foetal haemoglobin (F1) has been reported previously in the peripheral blood of foetal mice.

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Haemolysates of red blood cells from embryos of several developmental stages ranging from 2 to 21 incubation days and from post-hatching chickens of various age groups were analysed by ion-exchange chromatography, agar- and starch-gel electrophoresis, immuno-electrophoresis with specific antisera and polypeptide chain electrophoresis. With these methods two adult (A1 and A2) and six embryonic (E1–E6) haemoglobin types were identified. Antisera specific for the major adult haemoglobins (A1 and A2) as well as antisera specific for the major embryonic haemoglobins (E3, E4) could be prepared. Throughout embryogenesis the haemoglobin types contribute in varying amounts to the total haemoglobin pattern. Three periods of haemoglobin synthesis could be recognized, the transition between these periods occurred at the 6th and 12th incubation day. The first period is characterized by the presence of two major embryonic haemoglobins (E3 and E4) and two minor embryonic haemoglobins (E2 and E5). During the second period E3 and E4 are largely replaced by a major adult haemoglobin (A2) and a new embryonic haemoglobin (E1). The third period is characterized by the appearance of a second adult haemoglobin (A1) and a new minor embryonic haemoglobin (E6) with a concomitant decrease of E2 and E5. At the time of hatching two embryonic haemoglobins (E1 and E6) are still present. Besides A1 and A2, several minor haemoglobin fractions were inconsistently found in adult chickens. Evidence has been obtained that these additional fractions are reflecting a so called minor heterogeneity or separation artifacts. The haemoglobins A1, A2 and E1–E6 show different polypeptide chain compositions. Three embryo-specific chains could be demonstrated (β E2E5, γ E4 and δ E3). The production of the polypeptide chains appears to be correlated with the aforementioned periods of haemoglobin synthesis. The genetic and morphological implications of the findings are discussed.