Regulation of Heme Biosynthesis in Chick Embryo Liver Cells
According to current evidence heme controls the heme biosynthetic pathway primarily by controlling translocation of inactive pre-ALA-S from the cytosol into the mitochondrion, where ALA-S is active. A secondary mechanism involves inhibition by heme of transcription of the ALA-S gene. Porphyrinogenic drugs act by lowering a regulatory “free heme pool” by three different mechanisms: (a) by mechanism-based inactivation of cytochrome P-450 resulting in N-alkylprotoporphyrin formation and ferrochelatase inhibition, (b) by mechanism-based inactivation of cytochrome P-450 resulting in continuous heme destruction, (c) by enhanced generation of active oxygen species which interact with an endogenous substrate to form an inhibitor of uroporphyrinogen decarboxylase. It is also possible that porphyrinogenic drugs may exert a direct effect on the nucleus to increase formation of ALA-S mRNA.
The rate-controlling enzyme of the heme biosynthetic pathway is δ-aminolevulinic acid synthase (ALA-S). This enzyme which is located in the mitochondrion catalyzes the condensation of succinyl-CoA and glycine to form δ-aminolevulinic acid (ALA). ALA passes out of the mitochondria into the cytoplasm where two molecules condense together to form the pyrrole, porphobilinogen (PBG). The enzyme involved in catalyzing this reaction is δ-aminolevulinic acid dehydratase (ALA-D). PBG is converted to a linear tetrapyrrole by the enzyme porphobilinogen deaminase. The linear tetrapyrrole is transformed into uroporphyrinogen III (URO'GEN III) by the enzyme URO'GEN III co-synthetase (Fig. 1) URO'GEN III is then sequentially decarboxylated by the enzyme uroporphyrinogen decarboxylase (UROG-D) to coproporphyrinogen III (COPRO’GEN III), in the process 7-carboxy, 6-carboxy, and 5-carboxy intermediates are formed. After passage into the mitochondrion two of the propionic acid substituents of COPRO’GEN are converted to vinyl groups, yielding protoporphyrinogen IX (PROTO’GEN IX). In the next step of the pathway six hydrogen atoms are removed from PROTO’GEN IX, with the formation of protoporphyrin IX (PROTO IX). Ferrochelatase catalyzes the final step in the pathway, viz. the insertion of ferrous iron into PROTO IX to form heme1. The heme is subsequently incorporated into several hemoproteins with cytochrome P-450 synthesis requiring more than half of the heme produced. Heme exerts feedback repression on the synthesis of ALA-S. Normally this pathway is well controlled and very little of the intermediate porphyrinogens accumulate.
KeywordsHeme Biosynthesis Free Heme Heme Moiety Heme Biosynthetic Pathway Uroporphyrinogen Decarboxylase
Unable to display preview. Download preview PDF.
- 1.. Kappas, A., S. Sassa, K.E. Anderson. 1982. The porphyrias, In Stanbury, J.B., Wyngaarden, J.B., Fredrickson, D.S. (eds): The metabolic basis of inherited disease. New York, McGraw-Hill, p. 1301.Google Scholar
- 3.. Tyrrell, D.L.J., G.S. Marks. 1972. Drug-induced porphyrin biosynthesis V. Effect of protohemin on the transcriptional and post-transcriptional phases of 6-aminolevulinic acid synthetase induction. Biochem. Pharmacol. 21: 2077.Google Scholar
- 4.. Ades, I.Z., T.M. Stevens, P.D. Drew. 1987. Biogenesis of embryonic chick delta-aminolevulinate synthase: regulation of the level of mRNA by hemin. Arch. Biochem. Biophys. 253: 297.Google Scholar
- 5.. Hamilton, J.W., W.J. Bement, P.R. Sinclair, J.F. Sinclair, K.E. Wetterhahn. 1988. Expression of 5-aminolevulinate synthase and cytochrome P-450 mRNAs in chick embryo hepatocytes in vivo and in culture. Effect of porphyrinogenic drugs and haem. Biochem. J. 255: 267.Google Scholar
- 6.. May, B.K., I.A. Borthwick, G. Srivastava, B.A. Piróla, W.H. Elliott. 1986. Control of 5-aminolevulinate synthase in animals. Curr. Topics Cell. Regul. 28: 233.Google Scholar
- 8.. Yamamoto, M., N. Hayashi, G. Kikuchi. 1983. Translational inhibition by heme of the synthesis of hepatic 6-aminolevulinate synthase in a cell-free system. Biochem. Biophys. Res. Commun. 115: 225.Google Scholar
- 9.. Badawy, A.A.B., C.J. Morgan, N.R. Davis. 1985. Tryptophan pyrrolase and the regulation of mammalian heme biosynthesis, In: Nordmann Y. (ed): Porphyrins and Porphyrias. London, John Libbey Eurotext, INSERM, p. 69.Google Scholar
- 11.. Tephly, T.R., A.H. Gibbs, F. DeMatteis. 1979. Studies on the mechanism of experimental porphyria produced by 3,5-diethoxy-carbonyl-1,4-dihydrocollidine. Role of a porphyrin-like inhibitor of protohaem ferrolyase. Biochem. J. 180: 241.Google Scholar
- 15.. Tephly, T.R., B.L. Coffman, G. Ingall, G.S. Abou Zeit-Har, H.D. Tabba, K.M. Smith. 1981. Identification of N-methylprotoporphyrin IX in livers of untreated mice and mice treated with 3,5-die¬thoxycarbonyl- 1,4-dihydrocollidine: source of the methyl group. Arch. Biochem. Biophys. 212: 120.Google Scholar
- 16.. Augusto, 0., H.S. Beilan, P.R. Ortiz de Montellano. 1982. The catalytic mechanism of cytochrome P-450. Spin-trapping evidence for one-electron substrate oxidation. J. Biol. Chem. 257: 11288.Google Scholar
- 17.. Mackie, J.E., G.S. Marks. Synergistic induction of 6-amino- levulinic acid synthase activity by N-ethylprotoporphyrin IX and 3,5-diethoxycarbonyl-l,4-dihydro-2,6-dimethyl-4-isobutyl-pyridine. Biochem. Pharmacol. (In press).Google Scholar
- 18.. Farrel, G.C., M.A. Correia. 1980. Structural and functional reconstitution of hepatic cytochrome P-450 in. vivo • Reversal of allylisopropylacetamide-mediated destruction of the hemoprotein by exogenous heme. J. Biol. Chem. 255: 10128.Google Scholar
- 19.. Stejskal, R., M. Itabashi, J. Stanek, Z. Hruban. 1975. Experimental porphyria induced by 3-[2-(2,4,6-trimethylphenyl)-thioethyl]-4-methylsydnone. Virchows Arch. B. Cell. Path. 18: 83.Google Scholar
- 22.. Lukton, D., J.E. Mackie, J.E. Lee, G.S. Marks, P.R. Ortiz de Montellano. 1988. 2,2-Dialkyl-1,2-dihydroquinolines: cytochrome P-450 catalyzed N-alkylporphyrin formation, ferrochelatase inhibition, and induction of 5-aminolevulinic acid synthase activity. Chem. Res. Toxicol. 1: 208.Google Scholar
- 24.. DeMatteis, F. 1978. Loss of liver cytochrome P-450 caused by chemicals. Damage to the apoprotein and degradation of the heme moiety, In: DeMatteis, F., Aldridge, W.N, (eds): Handbook of experimental pharmacology, Vol. 44. Berlin. Springer-Verlag, p. 95.Google Scholar
- 26.. Lyon, M.E., J.A. Owen, G.S. Marks. 1988. Xenobiotic mediated inhibition of hepatic uroporphyrinogen decarboxylase activity in 17-day-old chick embryo liver cells in culture. Biochem. Pharmacol. 37: 1123.Google Scholar
- 27.. Billi, S.C, W. De Calmanovich, L.C. San Martin de Viale. 1986. Rat liver porphyrinogen carboxylase inhibitor as a function of the degree of hexachlorobenzene-induced porphyria, In: Morris, CR., Cabrai, J.R.D. (eds): Hexachlorobenzene: proceedings of an international symposium, Vol. 77. Lyon, IARC Scientific Publications, p. 487.Google Scholar
- 28.. Cantoni, L., D. Dal Fiume, H. Rizzardini, R. Ruggieri. 1984. In vitro inhibitory effect on porphyrinogen carboxylase of liver extracts from TCDD treated mice. Toxicol. Lett. 20: 211.Google Scholar
- 30.. Sinclair, P., R. Lambrecht, J. Sinclair. 1987. Evidence for a cytochrome P-450-mediated oxidation of uroporphyrinogen by cell-free extracts from chick embryos treated with 3-methylcholan-threne. Biochem. Biophys. Res. Commun. 146: 1324.Google Scholar