Ontogeny of haemoglobin in the chicken

Abstract

ABSTRACT The controversy as to whether haemoglobin embryology in the chicken involves qualitative or merely quantitative changes is settled by the observation of consistent electrophoretic differences between the haemoglobins of early embryos and the haemoglobins of foetuses, chicks and adult chickens. Studies on polypeptide chain composition indicate that the multiple haemoglobins of 3-to 5-day incubation embryos are A2C2, B2C2 and D2F2. The major and minor haemoglobins of foetuses and adult chickens are A2F2 and A2E2. Thus, although embryos and adults have no haemoglobins in common, they appear to have two kinds of polypeptide chains in common, A and F. Embryos have three unique polypeptide chain types and adults have one, on the basis of differences in electrophoretic mobility. Some degree of polypeptide chain interchange occurs with at least one of the chicken haemoglobins in that one of the adult haemoglobins will hybridize with human adult haemoglobin, α 2β 2. Although two of the three 3-to 5-day chick embryonic haemoglobin components have one of their polypeptide chain types in common with the major adult haemoglobin, the oxygen equilibria and Bohr effect of adult and early embryonic haemoglobin are very different. Chick embryo haemoglobin has an extremely high oxygen affinity and a Bohr effect only two-thirds that of the adult. The haemoglobin ‘switchover’ at the end of day 5 of incubation is not paralleled by changes in erythrocyte esterases, lactate dehydrogenase or malate dehydrogenase isoenzymes.