| Research Abstract |
It is generally accepted that almost 75% of heme produced in mammals are supplied for hemoglobin biosynthesis in the bone marrow. During erythroid differentiation the key enzyme for heme biosynthesis in the bone marrow, erythroid specific delta-aminolevulinate synthase, is regulated by erythroid type transcription factors, such as GATA-1 and NF-E2.
When we analyzed bone marrow ALAS-E activity from a patient with X-linked sideroblastic anemia, the level was as low as 10% of that in normal control. Western blot analysis, however, demonstrated a remarkable decrease in enzyme protein proportional to the enzyme activity defect. Thus, it is likely the patient has a mutation (s) to reduce the enzyme protein. Further investigations indicated that ALAS-E gene of the patient has Asp190Val mutation, whose protein expressed in QT-6 cells revealed a specific activity as high as the normal control enzyme with a relatively similar transcription-translation activity. We, therefore, examined effects of the mutation for mitchondrial transport of the enzyme. Although the mutated amino acid located approx. 100 amino acids downstream of the processing site of ALAS-E protein, the mutation resulted in 1.0 and 1.5 kDa larger size mature enzyme when compared with the normal protein (Furuyama, 1987).
We have also revealed that NF-E2, globin, and ALAS-E are controlled by Ras-Raf-MAP kinase signal transduction. Our analyzes clarified activate domain and suppress domain of NF-E2 were located within p45 and p18, respectively (Nagai, 1988).
As far as we examined nonspecific delta-aminolevulinate synthase (ALAS-N), the gene was negatively regulated via NF-KB binding sequence (Fujita, 1998).
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