Haem control in experimental porphyria. The effect of haemin on the induction of delta-aminolaevulinate synthase in isolated chick-embryo liver cells

• Published in: Biochemical journal Vol. 188; no. 3; pp. 781 - 788
• Main Authors: Srivastava, G, Brooker, J D, May, B K, Elliott, W H
• Format: Journal Article
• Language: English
• Published: England 15-06-1980
• Subjects: 5-Aminolevulinate Synthetase - antagonists & inhibitors; 5-Aminolevulinate Synthetase - biosynthesis; Allylisopropylacetamide - pharmacology; Animals; Chick Embryo; Enzyme Induction - drug effects; Heme - analogs & derivatives; Heme - metabolism; Hemin - pharmacology; In Vitro Techniques; Liver - drug effects; Liver - embryology; Liver - enzymology; Metabolism, Regulation and Control Processes; Porphyrias - metabolism
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj1880781

2-Allyl-2-isopropylacetamide-mediated induction of hepatic porphyria was studied in isolated chick-embryo liver cells. Increased delta-aminolaevulinate synthase activity occurred within 1h of induction and continued to increase for 8h. Protoporphyrins synthesized during this time accumulated to a concentration 10-fold greater than that in the control. Removal of 2-allyl-2-isopropylacetamide from the cells by washing at 3h immediately inhibited further increases in delta-aminolaevulinate synthase synthesis. However substitution of 2-allyl-2-isopropylacetamide at 3h by deferoxamine methane-sulphonate, an inhibitor of haem synthesis, allowed continued delta-aminolaevulinate synthase induction at an unaltered rate, even though this agent did not, by itself, induce enzyme synthesis. Exogenously added haemin was shown completely to inhibit 2-allyl-2-isopropylacetamide-mediated delta-aminolaevulinate synthase induction at concentrations as low as 20nm, a value that is less than the reported physiological one. The duration of inhibition was dependent on the concentration of added haemin and was followed by a period of delta-aminolaevulinate synthase synthesis at a rate similar to that of the control. These data are consistent with the hypothesis that delta-aminolaevulinate synthase synthesis is regulated by the concentration of intracellular haem and that induction is initiated by 2-allyl-2-isopropylacetamide-mediated destruction of haem. Induction of delta-aminolaevulinate synthase was shown to be dependent on both RNA and protein synthesis, and a study of the comparative effects of cordycepin, cycloheximide and haem has shown that, at haemin concentrations up to 50nm, the inhibition of delta-aminolaevulinate synthase synthesis followed kinetics similar to the effect of cordycepin, with no synergism between cordycepin and 50nm-haemin. However, at a haemin concentration of 2mum, the inhibition of delta-aminolaevulinate synthase synthesis followed similar kinetics to the effect of cycloheximide. These data demonstrate the control of delta-aminolaevulinate synthase synthesis by low concentrations of haemin and suggests that the primary effect of haemin is at the level of transcription.