EFFECT OF HEAVY METALS ON HEME AND CYTOCHROME P450

本提案的总体目的是调查 各种重金属对血红素和 P450超家族中的各种血红素蛋白。重金属如镉、镍、 铬、砷和铅诱导血红素加氧酶，血红素加氧酶是细胞内的限速酶。 血红素的降解和细胞色素P450水平的降低。先前 研究没有区分血红素加氧酶与金属的作用， 诱导氧化损伤的血红素和减少的分解， 细胞色素P450此外，金属可能会影响P450的合成。 铅和其他金属也影响血红素生物合成的不同步骤 通路铅增加尿中5-氨基乙酰丙酸（ALA）的分泌， 粪卟啉和锌原卟啉在网织红细胞中的积累。 其他重金属如As和Cd也被证明会影响 粪卟啉的排泄。锌原卟啉在铅中的富集 毒性归因于铁螯合酶掺入锌， 还原铁缺乏，而不是铁螯合酶抑制 活动本身。目前尚不清楚铅是如何导致这种缺乏的。 还原铁或金属如何介导粪卟啉的积累。 在本提案中，我们将调查： 1.血红素加氧酶诱导对重型颅脑损伤中氧化损伤的作用 金属-金属介导的肝血红素和细胞色素P450的降解。我们 并研究了重金属对P450合成的影响。 这些研究将使用大鼠肝细胞的原代培养物。 2.重金属抑制植物生长的机制 血红素生物合成途径的终端步骤，并增加积累 锌原卟啉和尿粪卟啉的排泄。的一部分 通过这些研究，我们希望能够确定细胞内 还原剂，以保持铁的还原，并防止氧化， 粪卟啉原转化为粪卟啉。这些调查将使用 大鼠和鸡肝细胞、大鼠肾细胞、兔 从大鼠肝脏和肾脏分离的红系细胞和线粒体。

The overall purpose of this proposal is to investigate the effects of various heavy metals ont the synthesis and degradation of both heme and various hemoproteins in the P450 superfamily. Heavy metals such as Cd, Ni, Cr, As and Pb induce heme oxygenase, the rate-limiting enzyme in the degradation of heme, and decrease levels of cytochrome P450. Previous studies have not distinguished the role of heme oxygenase versus metal- induced oxidative damage in the breakdown of heme and decrease in cytochrome P450. In addition, metals may affect the synthesis of P450. Pb and other metals also effect different steps of the heme biosynthetic pathway. Pb increases urinary secretion of 5-aminolevulinate (ALA) and coproporphyrin, and accumulation of zinc protoporphyrin in reticulocytes. Other heavy metals such as As and Cd have also been shown to affect excretion of coproporphyrin. Accumulation of zinc protoporphyrin in lead toxicity is attributed to incorporation of zinc by ferrochelatase due to deficiency of reduced iron, rather than to inhibition of ferrochelatase activity per se. It is not known how lead causes this deficiency of reduced iron or how metals mediate the accumulation of coproporphyrin. In this proposal, we will investigate: 1. The role of heme oxygenase induction versus oxidative damage in heavy metal-metal-mediated degradation of hepatic heme and cytochrome P450. We also will investigate the effect of heavy metals on the synthesis of P450. These studies will use primary cultures of rat hepatocytes. 2. The mechanisms underlying the effect of heavy metals to inhibit terminal steps of the heme biosynthetic pathway and increase accumulation of zinc protoporphyrin and excretion of urinary coproporphyrin. As part of these investigations, we expect to define the role of intracellular reductants to maintain reduction of Fe and prevent oxidation of coproporphyrinogen to coproporphyrin. These investigations will use primary cultures of rat and chick hepatocytes, rat kidney cells, rabbit erythroid cells and mitochondria isolated from rat liver and kidney.