CONVERSION OF 5-AMINOLAEVULINATE INTO HEME BY HOMOGENATES OF HUMAN-LIVER - COMPARISON WITH RAT AND CHICK-EMBRYO LIVER HOMOGENATES
CONVERSION OF 5-AMINOLAEVULINATE INTO HEME BY HOMOGENATES OF HUMAN-LIVER - COMPARISON WITH RAT AND CHICK-EMBRYO LIVER HOMOGENATES
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DOI：
10.1042/bj2270893
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发表时间：
1985-01-01
影响因子：
4.1
通讯作者：
SINCLAIR, JF
中科院分区：
文献类型：
--
作者：
BONKOVSKY, HL;HEALEY, JF;SINCLAIR, JF
为了评估是否可以在少量的人体肝脏中研究血红素的合成，在人体肝脏匀浆中测量了5-氨基乙酰丙酸转化为血红素及其前体的动力学。人肝匀浆转化5-氨基乙酰丙酸为原卟啉的最大速率仅为大鼠的26%，鸡胚胎的58%。在没有添加Fe2+的情况下，新鲜人肝匀浆中原卟啉和血红素的积累量与鸡胚相似，而新鲜大鼠肝匀浆中的血红素积累量约为原卟啉的两倍。当Fe2+(0.25 mM)加入到人肝匀浆中时，主要是血红素的积累，这表明还原铁的供应限制了血红素生物合成途径中的终末酶--血红素合成酶的活性。加入有效的铁络合剂去铁胺与5-氨基[14C]乙酰丙酸孵育30分钟后，停止了进一步的血红素合成，但不影响原卟啉的合成。加入去铁胺后，预先标记的亚铁血红素稳定。因为5-氨基[~(14)C]乙酰丙酸转化为血红素和原卟啉是在pH为7.4的条件下进行的，而大鼠或牛肝5-氨基乙酰丙酸脱水酶的最适pH为.apprx。6.3，测定了两种pH值下人肝脱水酶的动力学参数，而Km值在低pH时略高。从5-氨基乙酰丙酸合成卟啉和血红素，可以用经皮针刺活检获得的少量人体肝脏进行研究。本文还讨论了以大鼠或鸡胚肝为实验模型的结果对人类急性卟啉病生化特征的影响。
To assess whether the synthesis of heme can be studied in small amounts of human liver, the kinetics of the conversion of 5-aminolevulinate into heme and heme precursors was measured in homogenates of human livers. The maximal rate at which homogenates of human livers converted 5-aminolevulinate into protoporphyrin was only 26% of that for rat, and 58% of that for chick embryo. In the absence of added Fe2+, homogenates of fresh human liver resembled those of chick embryos in that protoporphyrin and heme accumulated in similar amounts, whereas fresh rat liver homogenate accumulated about twice as much heme as protoporphyrin. When Fe2+ (0.25 mM) was added to human liver homogenates, mainly heme accumulated, indicating that the supply of reduced Fe limited the activity of heme synthase, the final enzyme in the heme-biosynthesis pathway. Addition of the potent Fe chelator desferrioxamine after 30 min of incubation with 5-amino[14C]levulinate stopped further heme synthesis without affecting synthesis of protoporphyrin. The prelabeled heme was stable after addition of desferrioxamine. Since the conversion of 5-amino[14C]levulinate into heme and protoporphyrin was carried out at pH 7.4, whereas the pH optimum for rat or bovine hepatic 5-aminolevulinate dehydratase is .apprx. 6.3, kinetic parameters of the human hepatic dehydrase was determined at both pH values, whereas the Km was slightly higher at the lower pH. The synthesis of porphyrins and heme from 5-aminolevulinate can be studied with the small amounts of human liver obtainable by percutaneous needle biopsy. The implications of the results in relation to use of rat or chick-embryo livers as experimental models for the biochemical features of human acute porphyria are discussed.