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.

National Institute of Health (NIH)
National Institute of Environmental Health Sciences (NIEHS)
Research Project (R01)
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Study Section
Xenobiotic and Nutrient Disposition and Action Study Section (XNDA)
Program Officer
Carlin, Danielle J
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Louisiana State Univ Hsc New Orleans
Schools of Medicine
New Orleans
United States
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Reed, James R; Cawley, George F; Ardoin, Taylor G et al. (2014) Environmentally persistent free radicals inhibit cytochrome P450 activity in rat liver microsomes. Toxicol Appl Pharmacol 277:200-9
Johnson, Eric F; Connick, J Patrick; Reed, James R et al. (2014) Correlating structure and function of drug-metabolizing enzymes: progress and ongoing challenges. Drug Metab Dispos 42:9-22
Brignac-Huber, Lauren M; Reed, James R; Eyer, Marilyn K et al. (2013) Relationship between CYP1A2 localization and lipid microdomain formation as a function of lipid composition. Drug Metab Dispos 41:1896-905
Reed, James R; Cawley, George F; Backes, Wayne L (2013) Interactions between cytochromes P450 2B4 (CYP2B4) and 1A2 (CYP1A2) lead to alterations in toluene disposition and P450 uncoupling. Biochemistry 52:4003-13
Reed, James R; Backes, Wayne L (2012) Formation of P450 ยท P450 complexes and their effect on P450 function. Pharmacol Ther 133:299-310
Reed, James R; Cawley, George F; Backes, Wayne L (2011) Inhibition of cytochrome P450 1A2-mediated metabolism and production of reactive oxygen species by heme oxygenase-1 in rat liver microsomes. Drug Metab Lett 5:6-16
Brignac-Huber, Lauren; Reed, James R; Backes, Wayne L (2011) Organization of NADPH-cytochrome P450 reductase and CYP1A2 in the endoplasmic reticulum--microdomain localization affects monooxygenase function. Mol Pharmacol 79:549-57
Reed, James R; Eyer, Marilyn; Backes, Wayne L (2010) Functional interactions between cytochromes P450 1A2 and 2B4 require both enzymes to reside in the same phospholipid vesicle: evidence for physical complex formation. J Biol Chem 285:8942-52
Reed, James R; Huber 3rd, Warren J; Backes, Wayne L (2010) Human heme oxygenase-1 efficiently catabolizes heme in the absence of biliverdin reductase. Drug Metab Dispos 38:2060-6
Huber Iii, Warren J; Scruggs, Brittni A; Backes, Wayne L (2009) C-Terminal membrane spanning region of human heme oxygenase-1 mediates a time-dependent complex formation with cytochrome P450 reductase. Biochemistry 48:190-7

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