LEAD TOXICITY AND THE ALA-DEHYDRATASE POLYMORPHISM

-氨基乙酰丙酸脱水酶(ALAD，EC 4.2.1.4)是一种锌 铅对金属酶的抑制是第一个也是最敏感的 铅暴露的指标，其减少的活动已经很明显 与铅中毒的发病机制有关。这种酶的编码方式是 两个等位基因ALAD1(p=0.9)和ALAD2(q=0.1)。一种分子检测技术 已根据ALAD1的DNA序列进行了ALAD基因分型 ALAD-2等位基因。我们实验室的证据表明，铅- 暴露于ALAD-2杂合子或纯合子的个体有平均血液 铅水平比类似接触者高9微克/分升 ALAD1基因纯合。这些结果表明，从基因上讲， 易感人群，如果暴露在空气中，将面临更大的健康风险 在工作场所或环境中发挥领导作用。此外，由于铅是一种已知的 致畸因素，具有这种遗传易感性的女性的胎儿可能是 有较高的铅致先天畸形风险。在这 应用我们建议进行三项研究： 首先，研究ALAD等位基因与铅的关系 中毒将扩大到包括铅暴露的综合措施。 血铅是铅暴露的一种急性指标，并不衡量 最终保留的铅量。铅接触者ALAD基因分型的研究 人群也会与骨骼或乳牙本质铅有关 这两个指标都是铅暴露水平的综合衡量标准。 其次，将研究小鼠模型与(A)小鼠ALAD活动 和/或铅在体内组织或组织中的滞留和分布 (B)人体ALAD活性和/或浓度对铅的滞留和 在组织中的分布。这些模型将涉及(A)铅暴露。 具有不同ALAD基因剂量以及(B)的现有小鼠品系 表达人ALAD1或ALAD2等位基因的转基因小鼠。铅摄取， 铅的组织特异性分布及其对组织ALAD的抑制作用 将通过铅确定，以进一步澄清ALAD在以下方面的作用 铅中毒的病理生理学。 最后，将使用纯化的重组人ALAD同工酶来确定 它们对铅结合的不同亲和力、铅的抑制以及 蛋白水解酶抑制。重组同工酶也将被提供。 用于X射线测定它们的晶体结构。这些研究是 旨在确定差异遗传的生化基础 个人对铅暴露的易感性。

Delta-aminolevulinic acid dehydratase (ALAD, EC 4.2.1.4) is a zinc metalloenzyme whose inhibition by lead is the first and most sensitive indicator of lead exposure and whose decreased activity has been clearly implicated in the pathogenesis of lead poisoning. The enzyme is encoded by two alleles, ALAD1 (p = 0.9) and ALAD2 (q = 0.1). A molecular test for ALAD genotyping has been developed based on the DNA sequences of the ALAD1 and ALAD 2 alleles. Evidence from our laboratory indicates that lead- exposed individuals heterozygous or homozygous for ALAD 2 have mean blood lead levels 9 micrograms/dl greater than similarly exposed individuals homozygous for ALAD1. These results suggest that there are genetically susceptible individuals who would be at an increased health risk if exposed to lead in the workplace or environment. Moreover, since lead is a known teratogen, the fetuses of women with such a genetic susceptibility may be at higher risk for lead-induced congenital abnormalities. In this application we propose three studies: First, investigation of the relationship of the ALAD alleles to lead poisoning will be extended to include integrated measures of lead exposure. Blood lead is an acute measure of lead exposure and does not measure the amount of lead ultimately retained. ALAD genotypes in lead-exposed populations will also be related to bone or deciduous teeth dentine lead levels, both integrated measures of lead exposure. Second, mouse models will be investigated to relate (a) mouse ALAD activity and/or concentration to lead retention and distribution in body tissues or (b) human ALAD activity and/or concentration to lead retention and distribution in tissues. These models will involve lead exposure of (a) existing mouse strains with differing ALAD gene doses as well as (b) transgenic mice expressing the human ALAD1 or ALAD2 allele. Lead uptake, the tissue-specific distribution of lead and the inhibition of tissue ALAD by lead will be determined in order to clarify further the role of ALAD in the pathophysiology of lead poisoning. Finally, purified recombinant human ALAD isozymes will be used to determine their differential affinity for lead binding, inhibition by lead, and protease inhibition. The recombinant isozymes will also be made available for X-ray determination of their crystal structures. These studies are aimed at determining the biochemical basis for the differential genetic susceptibility of individuals to lead exposure.