Identification of five embryonic hemoglobins of rat and ontogeny of their constituent globins during fetal development.

Hemoglobins of rats switch from an embryonic to an adult type during fetal development. However, very little is known about the structures and molecular species of hemoglobins occurring in the fetal life of rats. In the present study we isolated five embryonic hemoglobins, designated E1, E2, E3, E4, and E5, from the blood of rat fetuses on day 14 of gestation by ion exchange chromatography. Reverse-phase high performance liquid chromatography revealed that these hemoglobins each consist of two kinds of globins: E1(11 alpha:epsilon 1), E2(1 alpha: epsilon 1), E3(zetta: epsilon 1), E4(1 alpha: epsilon 3), and E5(zetta: epsilon 3), respectively. The complete amino acid sequences of the zetta, epsilon 1, and epsilon 3 globins were determined. The zetta globin showed characteristic features common in alpha-type embryonic globins of known species in that the N-terminus is blocked and the amino acid at position 38 is Gln. epsilon 1 and epsilon 3 are beta-type embryonic globins, sharing 73.7% amino acid homology. Interestingly, they are more similar to the corresponding mouse beta-type embryonic globins, y and z, respectively, than to each other, implying that these globins have evolved orthologously from common ancestral proteins. It was also shown that the zetta, epsilon 1, and epsilon 3 globins are almost completely replaced by the adult type alpha and beta globins in the blood of rat fetuses by day 18 of gestation.