Srivastava G, Brooker J D, May B K, Elliott W H
Biochem J. 1980 Jun 15;188(3):781-8. 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.
在分离的鸡胚肝细胞中研究了2-烯丙基-2-异丙基乙酰胺介导的肝卟啉症诱导作用。诱导后1小时内δ-氨基乙酰丙酸合酶活性增加，并持续增加8小时。在此期间合成的原卟啉积累到比对照高10倍的浓度。在3小时时通过洗涤从细胞中去除2-烯丙基-2-异丙基乙酰胺立即抑制了δ-氨基乙酰丙酸合酶合成的进一步增加。然而，在3小时时用去铁胺甲磺酸盐（一种血红素合成抑制剂）替代2-烯丙基-2-异丙基乙酰胺，即使该试剂本身不诱导酶合成，也能使δ-氨基乙酰丙酸合酶以不变的速率持续诱导。外源性添加的血红素在低至20nm的浓度下就完全抑制了2-烯丙基-2-异丙基乙酰胺介导的δ-氨基乙酰丙酸合酶诱导，该值低于报道的生理值。抑制的持续时间取决于添加的血红素浓度，随后是一段时间的δ-氨基乙酰丙酸合酶合成，其速率与对照相似。这些数据与以下假设一致，即δ-氨基乙酰丙酸合酶的合成受细胞内血红素浓度的调节，并且诱导是由2-烯丙基-2-异丙基乙酰胺介导的血红素破坏引发的。已证明δ-氨基乙酰丙酸合酶的诱导依赖于RNA和蛋白质合成，对虫草素、环己酰亚胺和血红素的比较作用研究表明，在血红素浓度高达50nm时，δ-氨基乙酰丙酸合酶合成的抑制遵循与虫草素作用相似的动力学，虫草素和50nm血红素之间没有协同作用。然而，在血红素浓度为2μm时，δ-氨基乙酰丙酸合酶合成的抑制遵循与环己酰亚胺作用相似的动力学。这些数据证明了低浓度血红素对δ-氨基乙酰丙酸合酶合成的控制，并表明血红素的主要作用在转录水平。
