Toxicological Significance of Alkylbenzene Metabolism

描述(申请人提供)：这项建议的长期目标是更好地了解P450单加氧酶系统的蛋白质在内质网中是如何组织的，P450-P450相互作用对这些酶的功能的作用，以及这些相互作用如何通过P450介导的碳氢代谢的变化使个体容易受到烷基苯诱导的毒性。烷基苯在世界各地大量生产，简单的芳香烃是汽油的主要成分，用于各种消费品。P450系统负责芳香烃的脂肪族和芳香族羟基化，与碳氢化合物代谢有关的几种形式，如CYP1A2、CYP2B4和CYP2E1。这一过程需要P450和黄素蛋白NADPH-细胞色素P450还原酶之间的功能相互作用。然而，总P450水平超过还原酶的比例为20：1。这些条件提出了关于这种微粒体电子传递链的酶是如何组织的基本问题。在之前的授权期内，我们证明了P450通过形成异构体P450复合体来相互作用。我们已经确定了CYP2B4-CYP1A2和CYP1A2-CYP2E1之间的复合体。这些相互作用被证明对异物代谢有深远的影响，这主要是由于NADPH-细胞色素P450还原酶将电子转移到异构体复合体中的P450的方式的改变。有趣的是，我们没有观察到CYP2B4-CYP2E1复合体对P450功能的影响。拟议的研究旨在扩大我们的研究范围，并解决与还原酶和P450的组织、它们在内质网中的相互作用以及这些相互作用如何影响外源代谢，包括烷基苯的代谢有关的问题。我们计划继续我们对这些相互作用的描述，检查(1)P450-P450相互作用的功能后果，(2)通过确定负责P450-P450复合体形成的区域(S)来研究这些相互作用的结构基础，以及(3)组织对P450-P450复合体形成的影响(即这些相互作用如何影响它们在内质网中的区域分布)。这些研究将增加我们对P450电子传输链的组织方式的理解，并将为P450系统在芳香烃的生物活化和活性氧的产生中所起的作用提供新的重要信息-这一过程可以对化学毒性产生重大影响。与公共卫生相关：这项建议的目的是检查细胞内膜中P450系统的酶的组织。P450的组织方式不仅决定了它们从体内清除外来化合物的有效性，还决定了它们形成活性化合物的能力，这些化合物可能导致毒性、癌症和衰老。

DESCRIPTION (provided by applicant): The long-term objective of this proposal is to better understand how the proteins of the P450 monooxygenase system are organized in the endoplasmic reticulum, the role of P450-P450 interactions on the function of these enzymes, and how these interactions may make individuals susceptible to alkylbenzene-induced toxicity by alterations in P450-mediated hydrocarbon metabolism. Alkylbenzenes are produced in extensive quantities throughout the world, with simple aromatic hydrocarbons being major components of gasoline and used in a wide variety of consumer products. The P450 system is responsible for both aliphatic and aromatic hydroxylation of the aromatic hydrocarbons, with several forms, CYP1A2, CYP2B4, and CYP2E1, being implicated in hydrocarbon metabolism. This process requires a functional interaction between P450 and the flavoprotein NADPH-cytochrome P450 reductase. However, total P450 levels exceed those of reductase by a ratio of 20:1. These conditions raise basic questions as to how the enzymes of this microsomal electron transport chain are organized. During the previous grant period we demonstrated that P450s interact through the formation of heteromeric P450 complexes. We have identified complexes between CYP2B4-CYP1A2 as well as CYP1A2-CYP2E1. These interactions were shown to have a profound effect on xenobiotic metabolism, largely due to an alteration in the manner in which NADPH-cytochrome P450 reductase transfers electrons to P450s in the heteromeric complex. Interestingly, we did not observe an effect on P450 function from CYP2B4-CYP2E1 complexes. The proposed studies are designed to extend our investigation and address questions related to the organization of reductase and P450, their interactions within the endoplasmic reticulum, and how these interactions affect xenobiotic metabolism, including the metabolism of alkylbenzenes. We plan to continue our characterization of these interactions, examining (1) the functional consequences of P450-P450 interactions, (2) the structural basis for these interactions by identifying the region(s) responsible for P450-P450 complex formation, and (3) the organizational consequences to P450-P450 complex formation (i.e. how do such interactions affect their regional distribution in the endoplasmic reticulum). These studies will increase our understanding of how the P450 electron transport chain is organized, and will provide new important information on the role of the P450 system in the bioactivation of aromatic hydrocarbons and the generation of reactive oxygen - a process that can have a significant influence on chemical toxicity. PUBLIC HEALTH RELEVANCE: The purpose of this proposal is to examine the organization of the enzymes of the P450 system in membranes within the cell. How the P450s are organized will govern not only their effectiveness in removing foreign compounds from the body, but also their ability to form reactive compounds that can lead to toxicity, cancer, and aging.