ALAS2 is a specific erythroid isoform of 5-aminolevulinate synthetase (ALAS) and is essential for synthesis of hemoglobin in erythroid cells. Until recently, only mutations responsible for hereditary sideroblastic anemias had been reported. In the study of Whatley et al., 2 different deletions were detected (c.1706-1709 delAGTG and c.1699-1700 delAT) in exon 11 of the gene. These are responsible for alterations in amino acids 19 and 20 of the C-terminal extremity of the enzyme that causes structural change in the protein and in turn enhances its function. This is the first time a function-enhancing mutation has been identified in one of the enzymes involved in heme biosynthesis. With the increased functionality of the ALAS2 enzyme, which is the limiting enzyme of the metabolic pathway in normal conditions, ferrochelatase becomes the new limiting enzyme, leading to a greater accumulation of zinc protoporphyrin.
94PART II. BIOSYNTHESIS OF HEMOGLOBIN TABLE II% Uptake Few Experiment A Experiment B Control 29 52 Dialyzed (INTO) 9 16 Reconstituted 27 Glutathione ( 1 ~ 10 - 3M) 19 Glutathione ( 1 x 10~M) 52REFERENCES1~ Goldberg, A., Ashenbrucker, H., Cartwright, G. E., and Wintrobe, M. M.: Studieson the biosynthesis of heme in vitro by Adrian erythrocytes, Blood 11: 821, 1957.2. Schwartz, H. C., Cartwright, G. E., and Wintrobe, M. M.: Studies on the syn-thesis of heme from protoporphyrin, Clin. Research Proceedings 5: 29, 1957.3. Shemin, D., Abramsky, T., and Russell, C. S.: The synthesis of protoporphyrinfrom delta-amino levulinic acid in a cell-free extract, J. of the Am. Chem. Soc.76: 1, 1954.4. Krueger, R. C., Melnick, I., and Klein, J. R.: Formation of heme by broken-cellpreparations of duck erythrocytes, Arch. of Biochem. and Biophys. 64: 302, 1956.
Ferrochelatase (FECH) is an enzyme found in mitochondria that adds iron ions (Fe2+) into protoporphyrin to produce heme (Figure 1). This biochemical reaction is critical for cell health. The process is tightly controlled so that cells produce the amount of heme needed and do not accumulate too much of the heme precursor. The best-known protein that contains heme is hemoglobin, which is the oxygen-carrying protein in red blood cells. The ability of hemoglobin to carry oxygen depends on the iron in the heme cofactor. Heme is also present in proteins that function in mitochondrial energy production, in proteins that function in biochemical synthesis and degradation processes, and in proteins that detoxify hydrogen peroxide in cells.