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Ravula T, Barnaba C, Mahajan M, Anantharamaiah GM, Im SC, Waskell L, Ramamoorthy A. Membrane environment drives cytochrome P450's spin transition and its interaction with cytochrome b 5. Chem Commun (Camb) 2018; 53:12798-12801. [PMID: 29143058 DOI: 10.1039/c7cc07520k] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Heme's spin-multiplicity is key in determining the enzymatic function of cytochrome P450 (cytP450). The origin of the low-spin state in ferric P450 is still under debate. Here, we report the first experimental demonstration of P450's membrane interaction altering its spin equilibrium which is accompanied by a stronger affinity for cytochrome b5. These results highlight the importance of lipid membrane for the function of P450.
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Affiliation(s)
- Thirupathi Ravula
- Biophysics and Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA.
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2
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Kinetics of electron transfer between NADPH-cytochrome P450 reductase and cytochrome P450 3A4. Biochem J 2011; 432:485-93. [PMID: 20879989 DOI: 10.1042/bj20100744] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
We have incorporated CYP3A4 (cytochrome P450 3A4) and CPR (NADPH-cytochrome P450 reductase) into liposomes with a high lipid/protein ratio by an improved method. In the purified proteoliposomes, CYP3A4 binds testosterone with Kd (app)=36±6 μM and Hill coefficient=1.5±0.3, and 75±4% of the CYP3A4 can be reduced by NADPH in the presence of testosterone. Transfer of the first electron from CPR to CYP3A4 was measured by stopped-flow, trapping the reduced CYP3A4 as its Fe(II)-CO complex and measuring the characteristic absorbance change. Rapid electron transfer is observed in the presence of testosterone, with the fast phase, representing 90% of the total absorbance change, having a rate of 14±2 s(-1). Measurements of the first electron transfer were performed at various molar ratios of CPR/CYP3A4 in proteoliposomes; the rate was unaffected, consistent with a model in which first electron transfer takes place within a relatively stable CPR-CYP3A4 complex. Steady-state rates of NADPH oxidation and of 6β-hydroxytestosterone formation were also measured as a function of the molar ratio of CPR/CYP3A4 in the proteoliposomes. These rates increased with increasing CPR/CYP3A4 ratio, showing a hyperbolic dependency indicating a Kd (app) of ~0.4 μM. This suggests that the CPR-CYP3A4 complex can dissociate and reform between the first and second electron transfers.
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Li P, Zhu CL, Zhang XX, Gan L, Yu HZ, Gan Y. Reversible inhibitory effects of saturated and unsaturated alkyl esters on the carboxylesterases activity in rat intestine. Lipids 2010; 45:603-12. [PMID: 20532832 DOI: 10.1007/s11745-010-3434-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Accepted: 05/19/2010] [Indexed: 10/19/2022]
Abstract
This study was conducted to investigate the relationship between the carbon chain length/double bonds of alkyl esters and their inhibitory potency/mechanism on carboxylesterases (CESs). CESs activity was evaluated by inhibition of adefovir dipivoxil (ADV) metabolism in rat intestinal homogenates. Furthermore, the inhibitory effect of BNPP and ethyl (E)-hex-2-enoate (C8:1) on drug absorption was evaluated in situ intestinal perfusion model. The results showed that the rank order of the inhibitory potency on CESs was C10:0 > C8:0 > C6:0 > C4:0 > C12:0, C8:1 > C8:0, C6:1 > C6:0, while the esters (C14:0, C13:1, C16:0, C18:0, C17:1, C20:0) were found to have no inhibitory effect at investigated concentrations. However, the unsaturated esters (C20:1, C20:2, C20:3) displayed the inhibitory effect on CESs. Moreover, the double reciprocal plots indicated that alky esters inhibited the CESs in competitive and mixed competitive ways which were reversible. In addition, the result of most effective CESs inhibitor C8:1 from in situ experiment showed that C8:1 can inhibit the CESs-mediated intestinal metabolism and improve the drug absorption. And the inhibition had no time-dependent effect, compared with that of BNPP groups. The study suggested that alkyl esters can be served as effective and reversible CESs inhibitors, besides that their inhibitory potency/mechanism can be affected by their carbon chain length/double bonds.
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Affiliation(s)
- Ping Li
- Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai, 201203, China
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Expression of CYP4F2 in human liver and kidney: assessment using targeted peptide antibodies. Arch Biochem Biophys 2008; 478:59-68. [PMID: 18662666 DOI: 10.1016/j.abb.2008.06.025] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Revised: 06/21/2008] [Accepted: 06/24/2008] [Indexed: 02/01/2023]
Abstract
P450 enzymes comprising the human CYP4F gene subfamily are catalysts of eicosanoid (e.g., 20-HETE and leukotriene B4) formation and degradation, although the role that individual CYP4F proteins play in these metabolic processes is not well defined. Thus, we developed antibodies to assess the tissue-specific expression and function of CYP4F2, one of four CYP4F P450s found in human liver and kidney. Peptide antibodies elicited in rabbits to CYP4F2 amino acid residues 61-74 (WGHQGMVNPTEEG) and 65-77 (GMVNPTEEGMRVL) recognized on immunoblots only CYP4F2 and not CYP4F3b, CYP4F11 or CYP4F12. Immunoquantitation with anti-CYP4F2 peptide IgG showed highly variable CYP4F2 expression in liver (16.4+/-18.6pmol/mg microsomal protein; n=29) and kidney cortex (3.9+/-3.8 pmol/mg; n=10), with two subjects lacking the hepatic or renal enzyme entirely. CYP4F2 content in liver microsomes was significantly correlated (r> or =0.63; p<0.05) with leukotriene B4 and arachidonate omega-hydroxylase activities, which are both CYP4F2-catalyzed. Our study provides the first example of a peptide antibody that recognizes a single CYP4F P450 expressed in human liver and kidney, namely CYP4F2. Immunoquantitation and correlation analyses performed with this antibody suggest that CYP4F2 functions as a predominant LTB4 and arachidonate omega-hydroxylase in human liver.
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Yao HT, Chang YW, Lan SJ, Chen CT, Hsu JTA, Yeh TK. The inhibitory effect of polyunsaturated fatty acids on human CYP enzymes. Life Sci 2006; 79:2432-40. [PMID: 16978661 DOI: 10.1016/j.lfs.2006.08.016] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2006] [Revised: 07/19/2006] [Accepted: 08/10/2006] [Indexed: 11/24/2022]
Abstract
The inhibitory effect of saturated fatty acids (SFAs): palmitic acid (PA), stearic acid (SA) and polyunsaturated fatty acids (PUFAs): linoleic acid (LA), linolenic acid (LN), arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on six human drug-metabolizing enzymes (CYP1A2, 2C9, 2C19, 2D6, 2E1 and 3A4) was studied. Supersomes from baculovirus-expressing single isoforms were used as the enzyme source. Phenacetin O-deethylation (CYP1A2), diclofenac 4-hydroxylation (CYP2C9), mephenytoin 4-hydroxylation (CYP2C19), dextromethorphan O-demethylation (CYP2D6), chlorzoxazone 6-hydroxylation (CYP2E1) and midazolam 1-hydroxylation (CYP3A4) were used as the probes. Results show that all the five examined PUFAs competitively inhibited CYP2C9- and CYP2C19-catalyzed metabolic reactions, with Ki values ranging from 1.7 to 4.7 microM and 2.3 to 7.4 microM, respectively. Among these, AA, EPA and DHA tended to have greater inhibitory potencies (lower IC(50) and Ki values) than LA and LN. In addition, these five PUFAs also competitively inhibited the metabolic reactions catalyzed by CYP1A2, 2E1 and 3A4 to a lesser extent (Ki values>10 microM). On the other hand, palmitic and stearic acids, the saturated fatty acids, had no inhibitory effect on the activities of six human CYP isozymes at concentrations up to 200 microM. Incubation of PUFAs with CYP2C9 or CYP2C19 in the presence of NADPH resulted in the decrease of PUFA concentrations in the incubation mixtures. These results indicate that the PUFAs are potent inhibitors as well as the substrates of CYP2C9 and CYP2C19.
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Affiliation(s)
- Hsien-Tsung Yao
- Division of Biotechnology and Pharmaceutical Research, National Health Research Institutes, 35, Keyan Road, Zhunan Town, Miaoli County, Taiwan, ROC
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6
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Baas BJ, Denisov IG, Sligar SG. Homotropic cooperativity of monomeric cytochrome P450 3A4 in a nanoscale native bilayer environment. Arch Biochem Biophys 2004; 430:218-28. [PMID: 15369821 DOI: 10.1016/j.abb.2004.07.003] [Citation(s) in RCA: 145] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2004] [Revised: 06/29/2004] [Indexed: 11/28/2022]
Abstract
Mechanistic studies of mammalian cytochrome P450s are often obscured by the phase heterogeneity of solubilized preparations of membrane enzymes. The various protein-protein aggregation states of microsomes, detergent solubilized cytochrome or a family of aqueous multimeric complexes can effect measured substrate binding events as well as subsequent steps in the reaction cycle. In addition, these P450 monooxygenases are normally found in a membrane environment and the bilayer composition and dynamics can also effect these catalytic steps. Here, we describe the structural and functional characterization of a homogeneous monomeric population of cytochrome P450 3A4 (CYP 3A4) in a soluble nanoscale membrane bilayer, or Nanodisc [Nano Lett. 2 (2002) 853]. Cytochrome P450 3A4:Nanodisc assemblies were formed and purified to yield a 1:1 ratio of CYP 3A4 to Nanodisc. Solution small angle X-ray scattering was used to structurally characterize this monomeric CYP 3A4 in the membrane bilayer. The purified CYP 3A4:Nanodiscs showed a heretofore undescribed high level of homotropic cooperativity in the binding of testosterone. Soluble CYP 3A4:Nanodisc retains its known function and shows prototypic hydroxylation of testosterone when driven by hydrogen peroxide. This represents the first functional characterization of a true monomeric preparation of cytochrome P450 monooxygenase in a phospholipid bilayer and elucidates new properties of the monomeric form.
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Affiliation(s)
- Bradley J Baas
- Department of Biochemistry, University of Illinois Urbana-Champaign, 505 South Goodwin Avenue, IL 61801, USA
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Reed JR, Hollenberg PF. Examining the mechanism of stimulation of cytochrome P450 by cytochrome b5: the effect of cytochrome b5 on the interaction between cytochrome P450 2B4 and P450 reductase. J Inorg Biochem 2004; 97:265-75. [PMID: 14511889 DOI: 10.1016/s0162-0134(03)00275-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Dissociation constants K(d) for cytochrome P450 reductase (reductase) and cytochrome P450 2B4 are measured in the presence of various substrates. Aminopyrine increases the dissociation constant for binding of the two proteins. Furthermore, cytochrome b(5) (b(5)) stimulates metabolism of this substrate and dramatically decreases the substrate-related K(d) values. Experiments are performed to test if the b(5)-mediated stimulation is effected through a conformational change of P450. The effects of a redox-inactive analogue of b(5) (Mn b(5)) on product formation and reaction stoichiometry are determined. Variations in the concentration of Mn b(5) stock solution that have been shown to effect the aggregation state of the protein alter the rate of P450-mediated NADPH oxidation but have no effect on the rate of product formation. Thus, the electron transfer capability of b(5) is necessary for stimulation of metabolism. Furthermore, stopped flow spectrometry measurements of the rate of first electron reduction of the P450 by reductase indicate that the coupling of P450 2B4-mediated metabolism improves, in the presence of Mn b(5), with slower delivery of the first electron of the catalytic cycle by the reductase. These results are consistent with a model involving the regulation of the P450 catalytic cycle by conformational changes of the P450 enzyme. We propose that the conformational change(s) necessary for progression of the catalytic cycle is inhibited when reduced, but not oxidized, reductase is bound to the P450.
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Affiliation(s)
- James R Reed
- Department of Drug Metabolism, Merck and Co., PO Box 2000, Rahway, NJ 07065, USA.
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Reed JR, Hollenberg PF. Comparison of substrate metabolism by cytochromes P450 2B1, 2B4, and 2B6: relationship of heme spin state, catalysis, and the effects of cytochrome b5. J Inorg Biochem 2003; 93:152-60. [PMID: 12576277 DOI: 10.1016/s0162-0134(02)00597-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The metabolism of selected substrates by cytochromes P450 (P450) 2B1, 2B4, and 2B6 was compared, and the effects of cytochrome b(5) (b(5)) on these reactions were assessed. There did not appear to be any trends regarding the effects of b(5) when the metabolism of a given substrate by the different P450 enzymes was compared. The changes in spin states of the P450 enzymes as a result of interactions with substrates and cytochrome b(5) were also determined. Only P450 2B4 demonstrated a relationship between spin state, reaction coupling and b(5) effects. The rates of benzphetamine and 7-ethoxy-4-trifluoromethylcoumarin metabolism by the three enzymes could be correlated with the proportions of high spin heme. Similarly, the proportion of reaction coupling during the metabolism of selected substrates was approximately equal to the proportion of high spin P450. The data are interpreted to indicate that a P450 conformational equilibrium coordinately regulates catalysis and spin state changes.
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Affiliation(s)
- James R Reed
- Merck Research Laboratories, P.O. Box 2000, Mail Stop RY80L-109, Rahway, NJ 07065, USA.
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Abstract
The objective of the present study was to investigate whether or not different dietary oils, commonly used as drug vehicles, alter hepatic microsomal drug metabolism in the rat. Male adult Sprague-Dawley rats were administered 1 mL/kg/d of either corn, olive, sesame, or soybean oil via oral gavage for 7 days. An additional rat group was given an equal volume of water each day to serve as a control. We found that the hepatic cytochrome P450 (CYP) 3A2 protein level increased by 16% (p < 0.01) in rats given soybean oil compared with control rats. In contrast, CYP2C11 protein levels decreased by 32% (p < 0.01) in the corn oil group and by 31% (p < 0. 01) in rats given olive oil. The changes in the in vitro production of 6beta- and 2alpha-hydroxytestosterone, markers of CYP3A2 and 2C11 activities, respectively, were consistent with their protein levels, although not statistically different than controls. The results demonstrate that dietary oils may have differential effects on specific hepatic CYP isoforms and may add to the variability in metabolism when xenobiotics are administered using dietary oils as vehicles.
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Affiliation(s)
- L J Brunner
- Pharmaceutics Division, College of Pharmacy, PHR 4.214E, The University of Texas at Austin, Austin, Texas 78712-1074, USA.
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Harlow GR, Halpert JR. Analysis of human cytochrome P450 3A4 cooperativity: construction and characterization of a site-directed mutant that displays hyperbolic steroid hydroxylation kinetics. Proc Natl Acad Sci U S A 1998; 95:6636-41. [PMID: 9618464 PMCID: PMC22578 DOI: 10.1073/pnas.95.12.6636] [Citation(s) in RCA: 191] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/1998] [Indexed: 02/07/2023] Open
Abstract
Cytochrome P450 3A4 is generally considered to be the most important human drug-metabolizing enzyme and is known to catalyze the oxidation of a number of substrates in a cooperative manner. An allosteric mechanism is usually invoked to explain the cooperativity. Based on a structure-activity study from another laboratory using various effector-substrate combinations and on our own studies using site-directed mutagenesis and computer modeling of P450 3A4, the most likely location of effector binding is in the active site along with the substrate. Our study was designed to test this hypothesis by replacing residues Leu-211 and Asp-214 with the larger Phe and Glu, respectively. These residues were predicted to constitute a portion of the effector binding site, and the substitutions were designed to mimic the action of the effector by reducing the size of the active site. The L211F/D214E double mutant displayed an increased rate of testosterone and progesterone 6beta-hydroxylation at low substrate concentrations and a decreased level of heterotropic stimulation elicited by alpha-naphthoflavone. Kinetic analyses of the double mutant revealed the absence of homotropic cooperativity with either steroid substrate. At low substrate concentrations the steroid 6beta-hydroxylase activity of the wild-type enzyme was stimulated by a second steroid, whereas L211F/D214E displayed simple substrate inhibition. To analyze L211F/D214E at a more mechanistic level, spectral binding studies were carried out. Testosterone binding by the wild-type enzyme displayed homotropic cooperativity, whereas substrate binding by L211F/D214E displayed hyperbolic behavior.
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Affiliation(s)
- G R Harlow
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson, AZ 85721-0207, USA
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11
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Involvement of cytochrome P450 2E1 in the (ω–1)-hydroxylation of oleic acid in human and rat liver microsomes. J Lipid Res 1998. [DOI: 10.1016/s0022-2275(20)32545-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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12
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Ivanetich KM, Bradshaw JJ, Ziman MR. Delta 6-desaturase: improved methodology and analysis of the kinetics in a multi-enzyme system. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1292:120-32. [PMID: 8547334 DOI: 10.1016/0167-4838(95)00174-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
A new method of assay for the delta 6-desaturation of linoleic acid was developed. This method, which uses HPLC for separation of the fatty acid substrate and product, exhibited a lower coefficient of variation (0.3%) than the reported TLC method (3.5%), and avoided the step of methylation of the saponified fatty acid substrate and product. Using this new method of assay, the kinetics of the delta 6-desaturase in a multi-enzyme system were analysed. A number of factors that could have striking effects on desaturase kinetics were investigated, including the effect of (i) endogenous microsomal linoleic acid on total substrate concentration, and (ii) the pre-reaction catalysed by acyl-CoA synthetase and competing reactions catalysed by lysophospholipid acyltransferase and acyl-CoA hydrolase. Endogenous free linoleate in the hepatic microsomes was found to be 2.9 +/- 1.0 microM (0.5 mg microsomal protein/ml), which was comparable to added substrate concentrations (1.8 to 7.9 microM). The kinetics of the delta 6-desaturase were dissected from the kinetics of the above mentioned pre-reaction and competing reactions through a combination of experimental approaches and computer modeling. From computer modeling, a Km and Vmax of 1.5 microM and 0.63 nmol/min were calculated for the delta 6-desaturase, compared to Km and Vmax of 10.7 microM and 0.08 nmol/min calculated directly from data uncorrected for endogenous substrate. It was concluded that lysophospholipid acyltransferase, acyl-CoA synthetase and endogenous linoleic acid significantly affect the kinetic measurements of hepatic microsomal delta 6-desaturase. These results have implications for kinetic analyses of all desaturates in microsomal systems.
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Affiliation(s)
- K M Ivanetich
- Biomolecular Resource Center, University of California at San Francisco 94143-0541, USA
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Narasimhulu S. On the model controversy for substrate-induced spin-state transition in cytochrome P450: (a new perspective). Endocr Res 1993; 19:223-58. [PMID: 8306941 DOI: 10.1080/07435809309026680] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Three models have been proposed for substrate-induced spin-state transition in cytochrome P450. These are referred to as two-, three- and four-state models. In this communication the three models are reviewed with respect to their experimental basis and their ability to accommodate the results reported on the effects of substrates on spin-state and reduction of various P450's. In addition, a new perspective is presented.
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Affiliation(s)
- S Narasimhulu
- Harrison Department for Surgical Research, University of Pennsylvania, Philadelphia 19104
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14
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Iba MM, Gander JE, Mannering GJ. Lipid peroxidation-cytochrome P450 interactions. Use of linoleic acid hydroperoxide in the characterization of the spin-state of membrane-bound P450. Xenobiotica 1993; 23:227-39. [PMID: 8498086 DOI: 10.3109/00498259309059377] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
1. A procedure (linolenic acid hydroperoxide (LAHP) deletion method) is described in which LAHP is added to the reference cuvette of a pair of spectrally balanced cuvettes containing hepatic microsomes to produce a composite high spin (HS)-low spin (LS)-spectrum of P450. 2. The LAHP deletion method was used to determine the spin state of P450 in rat hepatic microsomes with and without the addition of type I compounds. 3. Advantage was taken of the temperature dependency of the spin state of P450 to determine the overall enthalpic and entropic changes for the spin equilibrium to generate computer-derived spectra of HS and LS forms of P450, and to construct a nomogram that allows direct estimation of the percentage of HS and LS spin forms of P450 in intact microsomes at temperatures compatible with biochemical functions. 4. The h.p.l.c. deletion method was used to demonstrate that HS-P450 comprised 57% of the P450 in hepatic microsomes; addition of type I substrates to these microsomes raised the level of HS-P450 to 97%. 5. The percentage of HS-P450 generated by the addition of type I compounds to microsomes declined with increasing deletions of P450 until at the extrapolated 100% level of deletion there was no HS-P450 above that of the original 57% observed in the absence of added compounds. This can be explained if LAHP destroys part of the LS-P450 while altering the remaining LS-P450 such that it retains its LS spectral characteristics but loses its capacity to form HS P450 when type I substrates are added. 6. These studies support the concept that about 50% of hepatic microsomal P450 is functionally in the HS state due to binding with high affinity endogenous substrates or other membrane components; the remaining P450 is LS-P450 that can bind to exogenous substrates to form HS-P450. 7. Applications of the LAHP deletion method for assessment of catalytic properties of membrane-bound P450 at ambient temperatures are discussed.
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Affiliation(s)
- M M Iba
- Department of Pharmacology, University of Minnesota School of Medicine, Minneapolis 55455
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15
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Omata Y, Friedman FK. The effect of dilauroyl-L-3-phosphatidylcholine on the interaction between cytochrome P-450 1A1 and benzo[a]pyrene. FEBS Lett 1992; 309:249-52. [PMID: 1516694 DOI: 10.1016/0014-5793(92)80782-c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Fluorescence quenching of benzo[a]pyrene (BP) by cytochrome P-450 1A1 was used to probe the effect of the lipid, dilauroyl-L-3-phosphatidylcholine, on this substrate-enzyme interaction. In the presence of lipid, a monoclonal antibody to this P-450 maximally inhibited BP binding at an antibody-to-P-450 ratio of 1:2, corresponding to an antibody crosslinked P-450 complex. The antibody did not inhibit BP binding in the absence of lipid. These results indicate that when P-450 is subjected to the orientational constraints imposed by antibody-mediated crosslinking, the lipid alters the conformation or quaternary structure of the P-450 oligomer in a manner which changes its affinity for BP.
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Affiliation(s)
- Y Omata
- Laboratory of Molecular Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892
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16
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Shah AB, Combes RD, Rowland IR. Interaction with microsomal lipid as a major factor responsible for S9-mediated inhibition of 1,8-dinitropyrene mutagenicity. Mutat Res 1991; 249:93-104. [PMID: 2067546 DOI: 10.1016/0027-5107(91)90135-b] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
1,8-Dinitropyrene (1,8-DNP), present in polluted air, is a rodent carcinogen and a potent, direct-acting mutagen in salmonella typhimurium TA98. This mutagenicity is markedly reduced in the presence of mammalian hepatic S9 or microsomes. We demonstrate that at least a substantial part of this effect is attributable to non-enzymatic processes. The microsomal-dependent inhibition was unaffected by omission of an NADPH-generating system or when the cytochrome P-450 inhibitor, SKF-525A, or the cytochrome P-448 inhibitor, ellipticine, was incorporated in the metabolic activation system, suggesting that mixed function oxidases are not involved. Heat inactivation partially decreased the ability of induced S9 to reduce DNP mutagenicity. Substitution of S9 with a similar concentration of bovine serum albumin did not affect DNP activity. Thus non-specific binding to microsomal protein is not involved. However, when lipids, derived from uninduced microsomes, were added to incubations of DNP and S. typhimurium TA98, mutagenicity was decreased. Furthermore, substitution of microsomal lipids with a suspension of phosphatidylcholine (PC), a major lipid constituent of microsomes, affected DNP mutagenicity similarly. An increase in PC concentration resulted in a greater inhibitory effect. The reduction in DNP mutagenicity observed with microsomal lipids or with PC was less than that detected with uninduced S9, whilst the mutagenicity of 2-nitrofluorene was reduced to an approximately equal extent by lipids and S9. This phenomenon may be responsible for the S9-mediated detoxification of other mutagenic nitroaromatic compounds and may have important implications for mutagenicity testing.
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Affiliation(s)
- A B Shah
- School of Biological Sciences, Portsmouth Polytechnic, Hampshire
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17
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Sartori E, Delaforge M. Specific drug binding to rat liver cytochrome P-450 isozymes induced by pregnenolone-16 alpha-carbonitrile and macrolide antibiotics. Implications for drug interactions. Chem Biol Interact 1990; 73:297-307. [PMID: 2107034 DOI: 10.1016/0009-2797(90)90010-k] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Clinical interactions of macrolides with various drugs lead to elimination impairment, increase of plasma concentration and overdose-like effects, resulting from modifications of their metabolism. Previous studies have shown that treatment of rats by the macrolide antibiotics of the oleandomycin and erythromycin series lead to the induction of an hepatic cytochrome P-450 which is implicated into their own metabolism. We have characterized PCN or macrolides induced cytochromes P-450 by their specific ability to interact with macrolide derivatives and, using the cytochrome P-450 spectral binding assays, we have shown that some compounds, implicated in drug interaction with macrolides, interact preferentially with the same cytochromes. This strongly suggests that specific blockage of cytochrome P-450 IIIA1 family by macrolides, is responsible for these drug interactions and that these interactions can be predicted easily by simple in vitro tests such as those described herein.
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Affiliation(s)
- E Sartori
- Université René Descartes, UA 400 CNRS, Laboratoire de Chimie et Biochimie, Paris, France
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Rietjens IM, Ancher LJ, Veeger C. On the role of phospholipids in the reconstituted cytochrome P-450 system. A model study using dilauroyl and distearoyl glycerophosphocholine. EUROPEAN JOURNAL OF BIOCHEMISTRY 1989; 181:309-16. [PMID: 2496984 DOI: 10.1111/j.1432-1033.1989.tb14725.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The difference in pentoxyresorufin O-dealkylating activity observed in a reconstituted system containing dilauroylglycerophosphocholine (Lau2GroPCho) or distearoylglycerophosphocholine (Ste2GroPCho) was used as a model to study the role of phospholipids in the reconstituted cytochrome P-450b (IIB1) system. The hypotheses proposed in the literature for the role of phospholipids in the reconstituted cytochrome P-450 system, mainly based on the comparison of systems without phospholipid and with Lau2GroPCho, were either validated or shown to be unlikely when tested by comparing reconstituted systems with different phosphatidylcholines. The higher activity in the Lau2GroPCho system as compared to the Ste2GroPCho system cannot be ascribed to (a) an increased affinity of cytochrome P-450 for the NADPH-cytochrome reductase in the Lau2GroPCho system, also not to (b) a Lau2GroPCho-dependent dissociation of protein multimers, nor to (c) a change in the spin state of the heme. We found a different apparent Km for pentoxyresorufin in the Lau2GroPCho system compared with the Ste2GroPCho system. Furthermore, we found a difference between the cytochrome P-450b tryptophan fluorescence polarization of the Lau2GroPCho system and the Ste2GroPCho system as well as with a system without phosphatidylcholine. From these observations it is concluded that the higher activity of the Lau2GroPCho system compared with the Ste2GroPCho system or with a system without additional phosphatidylcholine may at least in part be caused by a difference in the conformation of the cytochrome P-450 molecules in these systems. Furthermore, the different effects of both phosphatidylcholines on the Km and V for pentoxyresorufin not only suggest a role of phospholipids in the binding of the substrate to the active site of the cytochrome P-450 molecule, but also on the efficiency of electron transfer from NADPH-cytochrome reductase to cytochrome P-450.
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Affiliation(s)
- I M Rietjens
- Department of Biochemistry, Agricultural University, Wageningen, The Netherlands
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19
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Hsieh RJ, Kinsella JE. Oxidation of polyunsaturated fatty acids: mechanisms, products, and inhibition with emphasis on fish. ADVANCES IN FOOD AND NUTRITION RESEARCH 1989; 33:233-341. [PMID: 2697233 DOI: 10.1016/s1043-4526(08)60129-1] [Citation(s) in RCA: 234] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- R J Hsieh
- Campbell Institute for Research and Technology, Campbell Soup Company, Camden, New Jersey 08103
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20
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Romano MC, Straub KM, Yodis LA, Eckardt RD, Newton JF. Determination of microsomal lauric acid hydroxylase activity by HPLC with flow-through radiochemical quantitation. Anal Biochem 1988; 170:83-93. [PMID: 3389520 PMCID: PMC7119439 DOI: 10.1016/0003-2697(88)90093-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
An assay for the microsomal hydroxylation of lauric acid (LA), based on HPLC with flow-through radiochemical detection, has been developed. Conditions were optimized for resolution and quantitation of three microsomal metabolites of LA, one of which has not been reported previously as a metabolite of LA in mammalian microsomal incubations. These products, 12-(omega)-hydroxy-LA, 11-(omega-1)-hydroxy-LA, and a novel metabolite, 10-(omega-2)-hydroxy-LA, were isolated by HPLC and identified by gas chromatography/mass spectrometry. In the presence of NADPH, the formation of all three metabolites was linear with time and microsomal protein concentration. Hydrogen peroxide also supported the microsomal metabolism of LA, although the ratio of metabolites was substantially different than that produced by NADPH-supported microsomes. Several biochemical probes (metyrapone, alpha-naphthoflavone, 2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride, and 10-undecynoic acid) were used to dissociate the three LA hydroxylase activities. These experiments suggest that the site-specific hydroxylation [omega-, (omega-1)-, (omega-2)-] of LA may be catalyzed by different isozymes of cytochrome P-450.
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Affiliation(s)
- M C Romano
- Department of Drug Metabolism, Smith Kline & French Laboratories, Swedeland, Pennsylvania 19479
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21
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Abstract
The ways in which dietary polyunsaturated fats and antioxidants affect the balance between activation and detoxification of environmental precarcinogens is discussed, with particular reference to the polycyclic aromatic hydrocarbon benzo(a)pyrene. The structure and composition of membranes and their susceptibility to peroxidation is dependent on the polyunsaturated fatty acid (PUFA) content of the cell and its antioxidant status, both of which are determined to a large degree by dietary intake of these compounds. An increase in the PUFA content of membranes stimulates the oxidation of precarcinogens to reactive intermediates by affecting the configuration and induction of membrane-bound enzymes (e.g., the mixed-function oxidase system and epoxide hydratase); providing increased availability of substrates (hydroperoxides) for peroxidases that cooxidise carcinogens (e.g., prostaglandin synthetase and P-450 peroxidase); and increasing the likelihood of direct activation reactions between peroxyl radicals and precarcinogens. Antioxidants, on the other hand, protect against lipid peroxidation, scavenge oxygen-derived free radicals and reactive carcinogenic species. In addition some synthetic antioxidants exert specific effects on enzymes, which results in increased detoxification and reduced rates of activation. The balance between dietary polyunsaturated fats, antioxidants and the initiation of carcinogenesis is discussed in relation to animal models of chemical carcinogenesis and the epidemiology of human cancer.
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Affiliation(s)
- J D Gower
- Division of Comparative Medicine, Clinical Research Centre, Harrow, Middlesex, U.K
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22
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García-González M, Alejandre M, García-Peregrín E, Segovia J. Compensatory changes in the fatty acid composition of microsomal phospholipids induced by cholesterol feeding and further suppression. Nutr Res 1987. [DOI: 10.1016/s0271-5317(87)80033-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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23
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Davis HW, Suzuki T, Schenkman JB. Oxidation of esterified arachidonate by rat liver microsomes. Arch Biochem Biophys 1987; 252:218-28. [PMID: 3101595 DOI: 10.1016/0003-9861(87)90026-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Rat hepatic microsomal lipids were labeled with [U-14C]arachidonate and were then peroxidized by an NADPH-dependent iron pyrophosphate system. The extent of peroxidation was quantified by malondialdehyde production and arachidonate disappearance. Following peroxidation, the microsomes were centrifuged and the oxidation products were extracted from the supernatant. A linear correlation was found between malondialdehyde production and radioactivity in the supernatant. The pellet was treated with phospholipase A2 to cleave peroxidized products from the phospholipids. Exogenous phospholipase A2 activity was reduced by lipid peroxidation but this was overcome by using a high concentration of the enzyme along with the addition of melittin. The deesterified lipid products from the pellet were extracted and the fragments from the supernatant and the hydrolyzed pellet were separated by reverse-phase HPLC. Several different labeled polar products which coeluted with carbonyl-containing compounds (A285 and hydrazone formation) were found in both the supernatant and the pellet. In addition, many other carbonyl compounds were found which were not arachidonate-derived. The elution pattern of the fragments after 2 and 15 min of peroxidation were qualitatively identical; i.e., no product-precursor relationship was seen. This, along with the observation that peroxidation quickly ceased upon the rapid depletion of NADPH, suggests that propagation did not occur. Finally, the data indicate that cytochrome P-450 is not involved in microsomal lipid peroxidation since product formation is unaffected by the presence of carbon monoxide (80%) and no oxidation of phospholipid arachidonate occurs in the absence of iron.
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24
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Lewis DF, Tamburini PP, Gibson GG. The interaction of a homologous series of hydrocarbons with hepatic cytochrome P-450. Molecular orbital-derived electronic and structural parameters influencing the haemoprotein spin state. Chem Biol Interact 1986; 58:289-99. [PMID: 3742644 DOI: 10.1016/s0009-2797(86)80104-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The spectral interaction of a homologous series of alkyl-substituted benzenes and related compounds with purified mammalian cytochrome P-450 has been investigated. Each of the 10 hydrocarbons produced a Type I spectral change, indicative of a low to high spin transition of the haem iron of cytochrome P-450. The extent of perturbation of the cytochrome P-450 spin equilibrium varied for each compound and was used to quantify the spin shifts of the haemoprotein and consequently the substrate-bound spin equilibrium constant, K2. Molecular orbital calculations were utilised to determine the electronic structural parameters of the 10 hydrocarbons investigated, including the electrophilic and nucleophilic super-delocalizabilities summed over all atoms (sigma SE and sigma SN, respectively), the sum of the absolute values of net atomic charge (sigma QT) and the energy levels of both the highest occupied and lowest unoccupied molecular orbitals (E (HOMO) and E (LUMO) respectively). Multiple regression analyses were then utilized to generate quantitative structure-activity relationships between the above structural parameters and the substrate-bound spin equilibrium constant, K2. Good correlations were observed between sigma SE, sigma SN and sigma QT, indicating the importance of hydrophobicity and steric factors in the perturbation of the haemoprotein spin equilibrium. In addition, the electron-accepting potential of the hydrocarbons was an important structural feature and exhibited better correlations with K2 than the electron donating parameter. Taken collectively, our data show the importance of the hydrophobic and charge transfer characteristics of hydrocarbon substrates in dictating the position of the cytochrome P-450 spin equilibrium, and as such, provides a rational molecular explanation based on sound chemical principles for the differential interaction of hydrocarbons with cytochrome P-450.
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Gibson GG, Tamburini PP. Chemical modification of the histidine residues of purified hepatic cytochrome P-450: influence on substrate binding and the haemoprotein spin state. Chem Biol Interact 1986; 58:185-98. [PMID: 3719856 DOI: 10.1016/s0009-2797(86)80097-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
A hepatic cytochrome P-450 isolated in an electrophoretically homogeneous form from phenobarbital-treated rats, exists predominantly in the low spin configuration (82% at 20 degrees C). The addition of saturating amounts of the substrate benzphetamine to this haemoprotein shifted the spin equilibrium to the high spin form, resulting in a doubling of the spin equilibrium constant from 0.220 to 0.539 at 20 degrees C. The histidine residues of this low spin, substrate-free cytochrome P-450 were modified in a time- and concentration-dependent manner with diethylpyrocarbonate, and progressive histidine modification resulted in a decrease of both the affinity and extent of substrate interaction with the haemoprotein. Although the histidine-modified haemoprotein maintained the capacity to undergo a temperature-dependent spin transition of the haem iron in the presence of saturating amounts of substrate, this capability was substantially decreased in comparison to the unmodified cytochrome. These results indicate that a histidine residue(s) is involved in the binding of substrate to cytochrome P-450 and hence interferes with the substrate-bound spin equilibrium. Our results further imply that histidine is probably not the sixth ligand of the substrate-free ferric form of the rat liver cytochrome P-450.
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26
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Abstract
For a set of 10 para-substituted toluene derivatives, three enzymatic constants were determined describing their interaction with purified rabbit liver microsomal P-450LM2. The three constants were the catalytic rate constant (Kcat) for hydroxylation, the apparent dissociation constant (Kd) for the enzyme-substrate complex, and the interaction energy (delta Gint) between the substrate-binding and spin-state equilibria. The para-substituents of the toluene substrates were: hydrogen, fluoro, bromo, chloro, iodo, nitro, methyl, cyano, isopropyl, and t-butyl. Linear free energy correlations were sought between the enzymatic constants and several physical constants of the individual substrate molecules. These correlations would be useful both for empirical prediction purposes and for insight into active site chemistry and mechanics. Catalytic rates were correlated by a linear combination of the Hansch pi hydrophobic constant and the Hammett sigma value. A deuterium isotope effect (DV) of 2.6 for d8-toluene compared to d0-toluene confirmed that hydrogen abstraction was partially rate-limiting with this series of substrates. Apparent dissociation constants were predicted by a linear combination of the molar volume and pi, while the spin-state interaction energies were best predicted by a linear combination of the Hansch pi hydrophobic constant and the reciprocal of the dielectric constant.
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27
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Jansson I, Mole J, Schenkman JB. Purification and characterization of a new form (RLM2) of liver microsomal cytochrome P-450 from untreated rat. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(18)88891-3] [Citation(s) in RCA: 75] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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28
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Chemical characterization of protein-protein interactions between cytochrome P-450 and cytochrome b5. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(18)89223-7] [Citation(s) in RCA: 89] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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29
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Danis M, Kauffman FC, Evans RK, Holtzclaw D, Reinke LA, Thurman RG. Inhibition of p-nitroanisole O-demethylation in perfused rat liver by oleate. Biochem Pharmacol 1985; 34:609-16. [PMID: 3977941 DOI: 10.1016/0006-2952(85)90253-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
p-Nitroanisole O-demethylation in perfused livers from fasted, phenobarbital-treated rats was rapidly and reversibly inhibited by sodium oleate (0.3 to 0.6 mM). Xylitol partially reversed this inhibitory effect. The inhibition was not mediated by a direct effect of oleate on microsomal components since concentrations of oleate ranging up to 1.0 mM did not affect p-nitroanisole O-demethylation by isolated microsomes. Infusion of 0.6 mM oleate did not alter the measured intracellular NAD+/NADH ratio but did cause a significant increase in the intracellular NADP+/NADPH ratio. A significant decrease in the ATP/ADP ratio was also observed. Oleoyl CoA inhibited p-nitroanisole O-demethylation in microsomes (Ki about 30 microM), and both oleoyl CoA and palmitoyl CoA inhibited the energy-linked nicotinamide nucleotide transhydrogenase in submitochondrial particles (Ki about 1 microM). Thus, inhibition of mixed-function oxidation in the intact liver by oleate is most likely mediated by oleoyl CoA. Oleoyl CoA inhibits mixed-function oxidation in the intact liver by acting directly on cytochrome P-450 and by decreasing generation of NADPH via inhibition of key enzymes of the citric acid cycle and the energy-linked transhydrogenase.
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30
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Lake BG, Tredger JM, Gray TJ, Stubberfield CR, Hodder KD, Gangolli SD, Williams R. The effect of peroxisome proliferators on the metabolism and spectral interaction of endogenous substrates of cytochrome P-450 in rat hepatic microsomes. Life Sci 1984; 35:2621-6. [PMID: 6439971 DOI: 10.1016/0024-3205(84)90030-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The peroxisome proliferators clofibric acid and di-(2-ethylhexyl)-phthalate (DEHP) preferentially induced the 12-hydroxylation, compared to the 11-hydroxylation, of lauric acid in rat liver microsomes. A marked increase in the affinity of spectral interaction of this substrate with cytochrome P-450 was also observed. In addition, both clofibric acid and DEHP treatment produced a marked effect on the profile of site- and stereo-specific microsomal metabolites of testosterone. These results demonstrate that both peroxisome proliferators induce similar form(s) of cytochrome P-450 which are active in the metabolism of endogenous substrates of cytochrome P-450. The possible relevance of these findings to the hepatotoxicity of peroxisome proliferators is discussed.
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31
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Gibson GG, Tamburini PP. Cytochrome P-450 spin state: inorganic biochemistry of haem iron ligation and functional significance. Xenobiotica 1984; 14:27-47. [PMID: 6372266 DOI: 10.3109/00498258409151397] [Citation(s) in RCA: 36] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Haem ligation in cytochrome P-450 has been reviewed and the nature of the fifth and sixth ligands of the haemoprotein in the ferric low-spin, ferric high-spin, ferrous and ferrous-carbon-monoxy states have been discussed. Factors controlling the cytochrome P-450 spin equilibrium have been described, including substrate and functional components of the mixed-function oxidase system. In addition, a thermodynamic model describing the interaction of substrate with ferric cytochrome P-450 has been developed in terms of the micro-equilibrium constants governing substrate binding. The functional significance of the cytochrome P-450 spin state with particular reference to control of the first electron reduction of the haemoprotein has been summarized, and a subsequent validation of the spin-redox coupling model of cytochrome P-450-dependent catalysis has been presented.
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32
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Tamburini PP, Gibson GG. Thermodynamic studies of the protein-protein interactions between cytochrome P-450 and cytochrome b5. Evidence for a central role of the cytochrome P-450 spin state in the coupling of substrate and cytochrome b5 binding to the terminal hemoprotein. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(17)43934-2] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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33
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Saito K, Yamazoe Y, Kamataki T, Kato R. Interactions between the active metabolite of tryptophan pyrolysate mutagen, N-hydroxy-Trp-P-2, and lipids: the role of lipid peroxides in the conversion of N-hydroxy-Trp-P-2 to non-reactive forms. Chem Biol Interact 1983; 45:295-304. [PMID: 6411369 DOI: 10.1016/0009-2797(83)90076-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The interactions between lipids and the mutagenic active metabolite of 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) and 3-hydroxyamino-1-methyl-5H-pyrido[4,3-b]indole (N-hydroxy-Trp-P-2), were studied. Oleic acid showed an inhibitory effect on the formation of this active metabolite mainly by inhibition of hepatic microsomal oxidation systems. On the other hand, microsomal lipids from rat liver and commercial pig liver lecithin diminished the amount of N-hydroxy-Trp-P-2 without inhibiting the metabolism of Trp-P-2. The direct reaction of these lipids with N-hydroxy-Trp-P-2 was disclosed by experiments using N-hydroxy-Trp-P-2 and lipids without microsomes. Furthermore, the participation of lipid peroxides in this reaction was suggested by a linear relationship between the concentrations of the conjugated diene of lipids and the disappearance of N-hydroxy-Trp-P-2. When [3H]N-hydroxy-Trp-P-2 was incubated in the presence of pig liver lecithin, the polar products which were not formed in the incubation without lipids were newly detected by thin-layer chromatography (TLC) analysis.
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34
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Abstract
1. Hepatic microsomal drug metabolism determined with the substrates aniline (p-hydroxylation), ethylmorphine (N-demethylation) and p-nitrobenzoic acid (reduction), decreased during gestation in the rat to 53-73% of non-pregnant control levels by day 20 of gestation. 2. Enzyme activity remained low at one day post-partum, but had returned to control non-pregnant levels by five days post-partum. 3. The total capacity of the liver to metabolize drugs remained unchanged or increased because liver weight was increased by up to 40% during pregnancy. 4. Changes in drug metabolism were not related to alterations in the concentration, substrate-induced binding affinity (Ks) or maximal spectral change (delta Amax) of cytochrome P-450. 5. Alterations in hepatic drug metabolism are possibly mediated via changes in microsomal phospholipids and/or the cytochrome P-450 spin-state equilibrium as as pregnancy was associated with a decrease in (a) microsomal total phospholipids, (b) the phosphatidylcholine to phosphatidylethanolamine ratio and (c) the high-spin form of ferricytochrome P-450.
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35
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Heme ligand replacement reactions of cytochrome P-450. Characterization of the bonding atom of the axial ligand trans to thiolate as oxygen. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(19)81075-x] [Citation(s) in RCA: 91] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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36
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Hachino Y, Matsubara T, Hagihara B. pH-dependent interaction of microsomal cytochrome P-450 with substrates. I. Effect of pH upon the interaction of exogenous substrates with membrane-bound cytochrome P-450. Chem Biol Interact 1981; 37:181-90. [PMID: 7285242 DOI: 10.1016/0009-2797(81)90175-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The interaction of microsomal membrane-bound cytochrome P-450 with substrates was studied spectrophotometrically at various pH-values. The binding of type I compounds, hexobarbital and androstanedione, with cytochrome P-450, as determined by the magnitude of the type I spectral change of microsomes, was markedly enhanced at alkaline pH compared to that at acid pH. The pH-dependent spectral change could be reversed by changing the pH. The maximum absorption change (delta Amax) increased with increasing the pH, while the spectral dissociation constant (Ks) decreased. A similar pH-dependent binding reaction was also observed using a non-dissociative type I compound, cyclohexane. On the contrary, the absorbance magnitude between peak and trough in the aniline- or alcohol-induced difference spectrum of microsomes was enhanced by decreasing the pH, indicating easy complex formation of type II and reverse type I compounds with cytochrome P-450 in the acid rather than the alkaline region.
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37
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James JL, Clawson GA, Chan CH, Smuckler EA. Analysis of the phospholipid of the nuclear envelope and endoplasmic reticulum of liver cells by high pressure liquid chromatography. Lipids 1981; 16:541-5. [PMID: 7278515 DOI: 10.1007/bf02535053] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
A method is described for the separation and analysis of phospholipids from rat-liver nuclear envelope and endoplasmic reticulum. The procedure employs a liquid environment, to which antioxidants can be added, and results in separation of NL, PE, PI, PS, and PC in 99% purity in 12 min; analytical columns and a radial compression system may be employed. The procedure results in phospholipids with a large proportion of highly unsaturated fatty acids; some differences in fatty acid distributions were found when nuclear envelope phospholipid fractions were compared with the corresponding fractions from endoplasmic reticulum.
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Cunningham CC, Sinthusek G, Spach PI, Leathers C. Effect of dietary ethanol and cholesterol on phospholipid composition of hepatic mitochondria and microsomes from the monkey, Macaca nemestrina. Alcohol Clin Exp Res 1981; 5:417-26. [PMID: 7025694 DOI: 10.1111/j.1530-0277.1981.tb04925.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Monkeys (Macaca nemestrina) were divided into four groups, and each group was fed a particular diet. The variables in the diets were as follows: diet A, 0.3 mg cholesterol/kcal nutrient; diet B, 1.0 mg cholesterol/kcal nutrient; diet C, 0.3 mg cholesterol/kcal nutrient, ethanol (36% of calories); diet D, 1.0 mg cholesterol/kcal nutrient, ethanol (36% of calories). Monkeys on the diets containing ethanol developed fatty liver. Mitochondria and microsomes isolated from these livers demonstrated ethanol-elicited alterations in metabolic functions as is described in the preceding paper. Accompanying these changes in metabolic activities were alterations in organelle phospholipids that were influenced by both dietary ethanol and cholesterol. The changes that could be attributed to ethanol were as follows. Phosphatidyl ethanolamine was decreased in microsomes and increased in mitochondria; the sphingomyelin content in microsomes was increased significantly. The levels of stearic and arachidonic acid were elevated, and palmitic and oleic acid decreased, in phospholipids from both mitochondria and microsomes. Cholesterol influenced the fatty acid composition of several phospholipids, usually in a direction opposite to those alterations attributed to ethanol. Cholesterol feeding increased levels of palmitic and oleic acid and decreased amounts of stearic, linoleic, and arachidonic acid in several phospholipids. The significant ethanol- and cholesterol-elicited alterations observed in this study suggest the possibility that the changes in metabolic functions in mitochondria and microsomes are controlled, at least in part, by alterations in the phospholipid compositions of these organelles.
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Turcan RG, Tamburini PP, Gibson GG, Parke DV, Symons AM. Drug metabolism, cytochrome P450 spin state, and phospholipid changes during pregnancy in the rat. Biochem Pharmacol 1981; 30:1223-5. [PMID: 7271821 DOI: 10.1016/0006-2952(81)90301-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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40
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Normann PT, Thomassen MS, Christiansen EN, Flatmark T. Acyl-CoA synthetase activity of rat liver microsomes. Substrate specificity with special reference to very-long-chain and isomeric fatty acids. BIOCHIMICA ET BIOPHYSICA ACTA 1981; 664:416-27. [PMID: 7248332 DOI: 10.1016/0005-2760(81)90064-3] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
1. A fatty acid-depleted rat liver microsomal fraction has been used for the measurement of acyl-CoA synthetase (acid : CoA ligase (AMP-forming), EC 6.2.1.3) activity. The assay was based on measurement of the reaction product AMP by high-performance liquid chromatography (HPLC). The synthetase activity (V') revealed an optimum at 12 : 0 with saturated fatty acids as substrate, and at 14 : 1 with mono-unsaturated fatty acids. The apparent Michaelis constant, on the other hand, showed no systematic dependence on the fatty acid chain-length. 2. The mono-unsaturated fatty acids from 14 : 1 to 22 : 1 gave higher activities than the corresponding saturated fatty acids, and the relative differences were greatest with the very-long-chain fatty acids eicosaenoic (20 : 1 (11) (cis)) and docosaenoic acid (22 : 1 (11) (cis)). The synthetase activity with saturated and mono-unsaturated fatty acids was found to correlate to their capacity factor (k') on reversed phase chromatography (HPLC). This finding may indicate that the observed chain-length dependence of the activity largely reflects the partition of the fatty acids between a hydrophobic and a hydrophilic phase. In general, the position of the double bond and the cis/trans configuration had little effect on the V' values except for 22 : 1 (11)(cis) which revealed a 2-fold higher activity tha 22 : 1 (13) (cis). 3. The polyunsaturated fatty acid 22 : 6 (all cis) ;was notably found to be a much better substrate than other C22 fatty acids. 4. The present study does not support the idea of more than a single ATP-dependent acyl-CoA synthetase in the rat liver microsomal fraction.
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41
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42
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Moody DE, James JL, Smuckler EA. Cytochrome P-450 lowering effect of alkyl halides, correlation with decrease in arachidonic acid. Biochem Biophys Res Commun 1980; 97:673-9. [PMID: 7470119 DOI: 10.1016/0006-291x(80)90317-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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43
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