The molecular biology of mammalian hemoglobin synthesis.

The protein subunits of hemoglobin are made by the usual reactions of eukaryotic protein biosynthesis. Control of the rate, amount and kind of hemoglobin synthesis occurs at several levels. These include the transcription of globin messenger ribonucleic acid (mRNA), and the synthesis of other elements of the protein biosynthetic components. The translation of globin is restricted by mRNA abundance and possibly by mRNA structure, and by the availability and activity of the macromolecules required in protein synthesis. The process of red cell development provides a finite time during which the complement of hemoglobin can be synthesized. The events of red cell maturation include the enucleation of precursors, following which the biosynthetic components cannot be renewed, and the lability of the components imposes limitations on the duration of synthesis. The final result is mature erythrocytes which, in the healthy individual, are quite uniform and contain an average of 300 million hemoglobin molecules per cell with little excess of any of the hemoglobin moieties.