Cable E E, Gildemeister O S, Pepe J A, Donohue S E, Lambrecht R W, Bonkovsky H L
Department of Medicine, University of Massachusetts Medical Center, Worcester 01655, USA.
Eur J Biochem. 1996 Aug 15;240(1):112-7. doi: 10.1111/j.1432-1033.1996.0112h.x.
Hepatic 5-aminolevulinic acid synthase, the first and normally rate-controlling enzyme of heme biosynthesis, is regulated by heme. One of the known mechanisms whereby increased cellular heme regulates 5-aminolevulinic acid synthase is by decreasing the stability of its mRNA. In primary cultures of chick embryo liver cells, we tested whether a decrease in cellular heme might increase 5-aminolevulinic acid synthase mRNA stability and whether heme or other metalloporphyrins could reverse this stabilization. We found that: (a) The stability of 5-aminolevulinic acid synthase mRNA was markedly increased by inhibitors of heme biosynthesis, namely, 4,6-dioxoheptanoic acid or deferoxamine; (b) This increased stability of 5-aminolevulinic acid synthase mRNA was reversed by the addition of heme (10 microM) or by the combination of zinc mesoporphyrin (50 nM), an inhibitor of heme oxygenase, and heme (200 nM); (c) Repression of 5-aminolevulinic acid synthase mRNA levels by zinc mesoporphyrin (10 microM) was due to inhibition of heme oxygenase, rather than a direct, heme-like, effect of zinc mesoporphyrin on 5-aminolevulinic acid synthase mRNA; (d) Among the several non-heme metalloporphyrins tested, only zinc mesoporphyrin and chromium mesoporphyrin significantly decreased 5-aminolevulinic acid synthase mRNA without increasing heme oxygenase mRNA.
肝5-氨基酮戊酸合酶是血红素生物合成的首个且通常为限速酶，受血红素调控。细胞内血红素增加调控5-氨基酮戊酸合酶的已知机制之一是降低其mRNA的稳定性。在鸡胚肝细胞原代培养中，我们测试了细胞内血红素减少是否会增加5-氨基酮戊酸合酶mRNA的稳定性，以及血红素或其他金属卟啉是否能逆转这种稳定性。我们发现：(a) 血红素生物合成抑制剂，即4,6-二氧庚酸或去铁胺，可显著增加5-氨基酮戊酸合酶mRNA的稳定性；(b) 添加血红素（10微摩尔）或血红素加氧酶抑制剂锌卟啉（50纳摩尔）与血红素（200纳摩尔）的组合可逆转5-氨基酮戊酸合酶mRNA稳定性的增加；(c) 锌卟啉（10微摩尔）对5-氨基酮戊酸合酶mRNA水平的抑制是由于血红素加氧酶受到抑制，而非锌卟啉对5-氨基酮戊酸合酶mRNA有直接的、类似血红素的作用；(d) 在测试的几种非血红素金属卟啉中，只有锌卟啉和铬卟啉能显著降低5-氨基酮戊酸合酶mRNA，而不增加血红素加氧酶mRNA。
