Porphyrin biosynthesis in normal and disease states

描述（由申请人提供）：迟发性皮肤卟啉病（PCT）是人类最常见的卟啉病形式，与肝脏铁储存过量、酗酒、丙型肝炎和药用雌激素使用有关。PCT是由于肝脏中血红素生物合成酶尿卟啉原脱羧酶（URO-D）的比活性降低。我们已经确定，受损的催化活性的URO-D是由竞争性抑制剂指定uroporphomethene，八羧酸四吡咯大环与一个单一的氧化桥碳之间的两个吡咯环。桥碳的氧化由P450和铁依赖性反应介导。我们的第一个具体目标是确定卟啉亚甲基是通过羟甲基胆烷氧化产生的，然后非酶促环化，还是通过尿卟啉原氧化产生的，尿卟啉原是URO-D的完全还原底物。我们将测试的假设，即特定的P450和铁是需要产生的卟啉，通过排除野生型和突变酵母与功能性人类P450系统，并通过改变胞质铁浓度。我们的第二个具体目标将利用结构方法来定义卟啉介导的抑制机制，并确认我们的URO-D反应模型。我们的第三个具体目标是解决PCT中铁负荷的原因。我们将检验铁调素表达的抑制是过量肝脏铁储存的原因这一假设。总的来说，这些研究将定义参与PCT发病机制的分子机制，并解释在疾病相关风险因素发生率高的情况下PCT的相对罕见性。公共卫生相关性：迟发性皮肤卟啉病（PCT）的特征是一种化合物在肝脏中蓄积，该化合物通过血流移动到皮肤。这种被称为尿卟啉的化合物吸收太阳光，释放出损害皮肤的能量粒子。这种疾病是由于肝脏中的一种酶缺乏活性而引起的。我们已经确定，酶活性不足是由肝脏中存在过量铁时产生的抑制剂引起的。许多PCT患者因酗酒、丙型肝炎或使用某些激素而导致肝损伤。我们建议确定环境和遗传因素如何结合联合收割机，使酶抑制剂的发展。

DESCRIPTION (provided by applicant): Porphyria cutanea tarda (PCT), the most common form of porphyria in humans, is associated with excess liver iron stores, alcohol abuse, hepatitis C and medicinal estrogen use. PCT is due to a reduction in the specific activity of the heme biosynthetic enzyme uroporphyrinogen decarboxylase (URO-D) in the liver. We have determined that impaired catalytic activity of URO-D is caused by a competitive inhibitor designated uroporphomethene, an octacarboxylic tetrapyrrole macrocycle with a single oxidized bridge carbon between two of the pyrrole rings. Oxidation of the bridge carbon is mediated by P450 and iron dependent reactions. Our first specific aim is to determine if the porphomethene is generated by oxidation of hydroxymethyl bilane which then cyclizes non- enzymatically or by oxidation of uroporphyrinogen, the fully reduced substrate of URO-D. We will test the hypothesis that specific P450s and iron are required to generate the porphomethene by transfecting wild type and mutant yeast with functional human P450 systems and by altering cytosolic iron concentrations. Our second specific aim will utilize a structural approach to define the mechanism of porphomethene mediated inhibition and to confirm our model of the URO-D reaction. Our third specific aim will address the cause of iron loading in PCT. We will test the hypothesis that suppression of hepcidin expression is responsible for the excess liver iron stores. Collectively, these studies will define the molecular mechanisms involved in the pathogenesis of PCT and explain the relative rarity of PCT in face of the high incidence of disease associated risk factors. PUBLIC HEALTH RELEVANCE: Porphyria cutanea tarda (PCT) is characterized by accumulation in the liver of a compound that moves through the blood stream to the skin. The compound, called uroporphyrin, absorbs light from the sun and liberates energy particles that damage the skin. The disease is due to deficient activity of an enzyme in the liver. We have determined that deficient enzyme activity is caused by an inhibitor generated when excess iron is present in the liver. Many patients with PCT have liver damage from alcohol abuse, hepatitis C or from use of certain hormones. We propose to determine how environmental and genetic factors combine to allow the enzyme inhibitor to develop.