Sinclair P R, Sinclair J F, Bonkowsky H L, Gibbs A H, De Matteis F
Biochem Pharmacol. 1982 Mar 15;31(6):993-9. doi: 10.1016/0006-2952(82)90333-1.
Cobalt protoporphyrin generated from 5-amino[4-14C]laevulinate by homogenates or primary cultures of chick embryo liver exposed to CoCl2 was found to be radioactivity unextractable by acid/acetone, when extra protein was added. The activity of ferrochelatase was required for formation of cobalt protoporphyrin since inhibition of ferrochelatase with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (in the presence of cycloheximide) inhibited formation of cobalt protoporphyrin and resulted in accumulation of protoporphyrin. Cobalt protoporphyrin was detected spectrophotometrically in hepatocyte cultures exposed to the combination of 2-allyl-2-isopropylacetamide and CoCl2: (1) as the pyridine haemochrome of the protein pellet remaining after acid-acetone extraction of the cells, or (2) as the material extracted from the protein pellet with acetic acid-pyridine-chloroform. The amount of cobalt protoporphyrin increased with increasing CoCl2 concentration as cellular haem declined. The decrease in haem was about equal to the amount of cobalt protoporphyrin that accumulated. 2-Allyl-2-isopropylacetamide and polychlorinated biphenyls were both powerful inducers of 5-aminolaevulinate synthase. The former led to protoporphyrin accumulation, whereas with the latter, uroporphyrin accumulated, probably due to a concomitant decrease in activity of uroporphyrinogen decarboxylase. The decrease in activity of 5-aminolaevulinate synthase produced by administration of CoCl2 was greater after treatment with 2-allyl-2-isopropylacetamide than after treatment with allylisopropylacetamide and 3,4,3',4'-tetrachlorobiphenyl. We conclude: (a) that cobalt protoporphyrin is readily formed in cultured hepatocytes, and (b) that its formation accounts for the action of cobalt on 5-aminolaevulinate synthase.
当添加额外蛋白质时，发现由暴露于氯化钴的鸡胚肝匀浆或原代培养物从5-氨基[4-¹⁴C]δ-氨基乙酰丙酸生成的钴原卟啉是不能被酸/丙酮提取的放射性物质。钴原卟啉的形成需要亚铁螯合酶的活性，因为用3,5-二乙氧基羰基-1,4-二氢可力丁（在环己酰亚胺存在下）抑制亚铁螯合酶会抑制钴原卟啉的形成并导致原卟啉积累。在暴露于2-烯丙基-2-异丙基乙酰胺和氯化钴组合的肝细胞培养物中，通过分光光度法检测到钴原卟啉：（1）作为细胞经酸-丙酮提取后剩余蛋白质沉淀的吡啶血色原，或（2）作为从蛋白质沉淀中用乙酸-吡啶-氯仿提取的物质。随着细胞血红素下降，钴原卟啉的量随氯化钴浓度增加而增加。血红素的减少量约等于积累的钴原卟啉的量。2-烯丙基-2-异丙基乙酰胺和多氯联苯都是5-氨基乙酰丙酸合酶的强大诱导剂。前者导致原卟啉积累，而后者则导致尿卟啉积累，这可能是由于尿卟啉原脱羧酶活性同时降低所致。用2-烯丙基-2-异丙基乙酰胺处理后，氯化钴给药引起的5-氨基乙酰丙酸合酶活性降低比用烯丙基异丙基乙酰胺和3,4,3',4'-四氯联苯处理后更大。我们得出结论：（a）钴原卟啉在培养的肝细胞中很容易形成，（b）其形成解释了钴对5-氨基乙酰丙酸合酶的作用。
