Hemoglobin synthesis chick embryo blastoderm

C. The Chick Embryo Blastoderm System and Hemoglobin Synthesis... 

In the case of hemoglobin it is well documented that heme or its precursor, ALA, stimulates hemoglobin synthesis when added to preparations of hemolyzed bird erythrocytes, mammalian reticulocytes, or chick embryo blastoderm [6,7]. 

Fig. 9. Hypothesis on the control of hemoglobin synthesis in chick embryo blastoderm by control of the synthesis of ALA-synthetase. In the nucleus a repressor protein (I) blocks transcription, and a 5jS-H steroid acts as a derepressor, permitting the structural gene (II) to code for the mRNA of ALA-synthetase. In the cytoplasm the information in the mRNA is translated into the enzyme ALA-synthetase (E,) which migrates into the mitochondrion where ALA (III) is made and finally converted by other enzymes (E2-E7) to heme (IV). Heme controls the synthesis of globin either by acting at the initiating site or by permitting proper folding of the globin.

It was found by Levere et ah [137] that the same 5)6-H steroids that actively stimulated the synthesis of ALA-synthetase in chick embryo liver cells in culture also stimulated hemoglobin synthesis in chick embryo blastoderm cells (Fig. 9). It is inferred that the stimulation by the steroids is brought about by the same mechanism as for the liver cells that is, the steroids induce the synthesis of ALA-synthetase at the transcriptional level. ALA-synthetase is the rate-limiting enzyme in early red cell precursors, and its increase causes an earlier increase in the formation of ALA the ALA, once made, is rapidly converted to heme, and once heme is made globin is synthesized. Thus the controlling step in hemoglobin synthesis appears to be one that is turned on by a 5y -H steroid. Stimulation of hemoglobin synthesis by Sfi-H steroids has recently also been demonstrated in mice and in humans [140,142],... 

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