EFFECT OF HEAVY METALS ON HEME AND CYTOCHROME P450

这项提案的总体目的是调查 不同重金属对亚铁血红素和亚铁血红素合成和降解的影响 P450超家族中的各种血球蛋白。重金属，如Cd、Ni、 铬、砷和铅诱导的血红素加氧酶是植物生长发育的限速酶。 血红素降解，细胞色素P450水平下降。上一首 研究还没有区分血红素加氧酶和金属的作用- 在血红素分解中诱导氧化损伤和减少 细胞色素P450。此外，金属可能会影响P450的合成。 铅和其他金属也会影响血红素生物合成的不同步骤 路径。铅增加尿中5-氨基乙酰丙酸(ALA)和 和锌原卟啉在网织红细胞中的积累。 其他重金属，如砷和镉，也被证明影响 排泄共比例的卟啉。锌原卟啉在铅中的积累 毒性归因于铁络合酶结合锌，这是由于 缺乏还原的铁，而不是抑制铁络合酶 活动本身。目前尚不清楚铅是如何导致这一缺陷的 还原铁或金属如何调节共比例卟啉的积累。 在这项建议中，我们将调查： 1.血红素加氧酶诱导与氧化损伤的关系 金属-金属介导的肝血红素和细胞色素P450的降解。我们 还将研究重金属对P450合成的影响。 这些研究将使用大鼠肝细胞的原代培养。 2.重金属抑制作用的机制 血红素生物合成途径的末端步骤和增加积累 锌原卟啉和尿辅酶原卟啉排泄量。作为以下内容的一部分 这些研究，我们期望确定细胞内的作用 用于保持铁的还原和防止氧化的还原剂 共比例卟啉原到共比例卟啉。这些调查将利用 大鼠、鸡肝细胞、大鼠肾细胞、兔的原代培养 从大鼠肝、肾中分离出红系细胞和线粒体。

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.