Maines M D, Kappas A
J Biol Chem. 1975 Jun 10;250(11):4171-7.
The administration of cobalt to rats caused a marked increase in the oxidative degradation of heme (hematin, iron protoporphyrin-IX) BY HEPATIC MICROSOMAL ENZYMES. The onset of this enzyme stimulation was very rapid, beginning within 2 hours after injection of the metal and reaching its maximum in 16 to 24 hours. During the rapid phase of stimulation, i.e. the first 2 to 4 hours, when heme oxidation was 450% above control values, there was a significant decrease in microsomal oxidative N-demethylation activity and in microsomal oxidative Ndemethylation activity and in microsomal content of heme with an insignificant decrease in cytochrome P-450 content. Within 24 hours the oxidative activity of the microsomal electron transport chain for drugs was decreased to about 30% of the control. However, during the same period the oxidation of heme approached levels 800% above control. During this period there was a further decrease in the microsomal content of heme with a significant decrease in cytochrome P-450 content and an increase in the activity of delta-aminolevulinate synthetase. The activity of delta-aminolevulinate synthetase reached its maximum within 8 hours after cobalt treatment. Repeated injections (at 24-hour intervals) of cobalt were necessary to maintain these changes in microsomal enzyme activities since, after single injections of the metal, these parameters returned to normal within 72 hours. The inducing effect of cobalt on the oxidation of heme could be inhibited by the administration of actinomycin D and puromycin. Furthermore, this stimulatory effect could not be elicited by in vitro treatment of microsomes with cobalt nor could the effect be attributed to any soluble components of the cytoplasm. Cobalt protoporphyrin-IX was less effective than cobalt chloride in stimulating heme oxidation. 3-Amino-1, 2, 4-triazole did not enhance hepatic heme oxidation activity, while allylisopropylacetamide decreased this activity. The oxidative degradation of heme was found not to be cytochrome P-450 dependent since the highly increased levels of heme oxidation in microsomes from cobalt-treated animals could be retained despite the fact that the cytochrome P-450 content of such microsomes was decreased to spectrally undetectable amounts and drug oxidation was eliminated by treatment of the microsomes with 4 M urea. These findings exclude an obligatory role for cytochrome P-450 in the oxidation of heme compounds, although the possibility that this process is a heme-dependent oxidation is not ruled out.
给大鼠施用钴会导致肝脏微粒体酶对血红素（高铁血红素、铁原卟啉 - IX）的氧化降解显著增加。这种酶刺激的起始非常迅速，在注射金属后2小时内开始，并在16至24小时内达到最大值。在刺激的快速阶段，即最初的2至4小时，当血红素氧化比对照值高450%时，微粒体氧化N - 去甲基化活性以及微粒体血红素含量显著下降，而细胞色素P - 450含量下降不显著。在24小时内，微粒体电子传递链对药物的氧化活性降至对照值的约30%。然而，在同一时期，血红素的氧化接近比对照高800%的水平。在此期间，微粒体血红素含量进一步下降，细胞色素P - 450含量显著下降，δ - 氨基乙酰丙酸合成酶活性增加。δ - 氨基乙酰丙酸合成酶的活性在钴处理后8小时内达到最大值。由于单次注射金属后这些参数在72小时内恢复正常，因此需要重复注射（每隔24小时）钴以维持微粒体酶活性的这些变化。钴对血红素氧化的诱导作用可被放线菌素D和嘌呤霉素抑制。此外，用钴对微粒体进行体外处理不能引发这种刺激作用，该作用也不能归因于细胞质的任何可溶性成分。钴原卟啉 - IX在刺激血红素氧化方面比氯化钴效果差。3 - 氨基 - 1,2,4 - 三唑不会增强肝脏血红素氧化活性，而烯丙基异丙基乙酰胺会降低这种活性。发现血红素的氧化降解不依赖于细胞色素P - 450，因为尽管钴处理动物的微粒体中细胞色素P - 450含量降至光谱检测不到的量且通过用4 M尿素处理微粒体消除了药物氧化，但此类微粒体中血红素氧化水平仍高度升高。这些发现排除了细胞色素P - 450在血红素化合物氧化中的必然作用，尽管不排除该过程是血红素依赖性氧化的可能性。
