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Zhang X, Li XX, Liu Y, Wang Y. Suicide Inhibition of Cytochrome P450 Enzymes by Cyclopropylamines via a Ring-Opening Mechanism: Proton-Coupled Electron Transfer Makes a Difference. Front Chem 2017; 5:3. [PMID: 28197402 PMCID: PMC5281577 DOI: 10.3389/fchem.2017.00003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2016] [Accepted: 01/10/2017] [Indexed: 01/27/2023] Open
Abstract
N-benzyl-N-cyclopropylamine (BCA) has been attracting great interests for decades for its partial suicide inactivation role to cytochrome P450 (P450) via a ring-opening mechanism besides acting as a role of normal substrates. Understanding the mechanism of such partial inactivation is vital to the clinical drug design. Thus, density functional theoretical (DFT) calculations were carried out on such P450-catalyzed reactions, not only on the metabolic pathway, but on the ring-opening inactivation one. Our theoretical results demonstrated that, in the metabolic pathway, besides the normal carbinolamine, an unexpected enamine was formed via the dual hydrogen abstraction (DHA) process, in which the competition between rotation of the H-abstracted substrate radical and the rotation of hydroxyl group of the protonated Cpd II moiety plays a significant role in product branch; In the inactivation pathway, the well-noted single electron transfer (SET) mechanism-involved process was invalidated for its high energy barrier, a proton-coupled electron transfer [PCET(ET)] mechanism plays a role. Our results are consistent with other related theoretical works on heteroatom-hydrogen (X-H, X = O, N) activation and revealed new features. The revealed mechanisms will play a positive role in relative drug design.
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Affiliation(s)
- Xiaoqian Zhang
- College of Physics and Materials Science, Henan Normal University Xinxiang, China
| | - Xiao-Xi Li
- State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences Lanzhou, China
| | - Yufang Liu
- College of Physics and Materials Science, Henan Normal University Xinxiang, China
| | - Yong Wang
- State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences Lanzhou, China
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van Lier JE, Mast N, Pikuleva IA. Cholesterol Hydroperoxides as Substrates for Cholesterol-Metabolizing Cytochrome P450 Enzymes and Alternative Sources of 25-Hydroxycholesterol and other Oxysterols. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201505002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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3
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van Lier JE, Mast N, Pikuleva IA. Cholesterol hydroperoxides as substrates for cholesterol-metabolizing cytochrome P450 enzymes and alternative sources of 25-hydroxycholesterol and other oxysterols. Angew Chem Int Ed Engl 2015; 54:11138-42. [PMID: 26230055 PMCID: PMC4578806 DOI: 10.1002/anie.201505002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2015] [Indexed: 12/20/2022]
Abstract
The interaction of the primary autoxidation products of cholesterol, namely 25- and 20ξ-hydroperoxides, with the four principal cholesterol-metabolizing cytochrome P450 enzymes is reported. Addition of cholesterol 25-hydroperoxide to the enzymes CYP27A1 and CYP11A1 induced well-defined spectral changes while generating 25-hydroxycholesterol as the major product. The 20ξ-hydroperoxides induced spectral shifts in CYP27A1 and CYP11A1 but glycol metabolites were detected only with CYP11A1. CYP7A1 and CYP46A1 failed to give metabolites with any of the hydroperoxides. A P450 hydroperoxide-shunt reaction is proposed, where the hydroperoxides serve as both donor for reduced oxygen and substrate. CYP27A1 was shown to mediate the reduction of cholesterol 25-hydroperoxide to 25-hydroxycholesterol, a role of potential significance for cholesterol-rich tissues with high oxidative stress. CYP27A1 may participate in the removal of harmful autoxidation products in these tissues, while providing a complementary source of 25-hydroxycholesterol, a modulator of immune cell function and mediator of viral cell entry.
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Affiliation(s)
- Johan E van Lier
- Department of Nuclear Medicine and Radiobiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC, J1H 5N4 (Canada).
| | - Natalia Mast
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106 (USA)[*]Corresponding authors
| | - Irina A Pikuleva
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106 (USA)[*]Corresponding authors.
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Wang Y, Yang C, Wang H, Han K, Shaik S. A new mechanism for ethanol oxidation mediated by cytochrome P450 2E1: bulk polarity of the active site makes a difference. Chembiochem 2008; 8:277-81. [PMID: 17219453 DOI: 10.1002/cbic.200600510] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Yong Wang
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
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Borowski T, de Marothy S, Broclawik E, Schofield CJ, Siegbahn PEM. Mechanism for Cyclization Reaction by Clavaminic Acid Synthase. Insights from Modeling Studies. Biochemistry 2007; 46:3682-91. [PMID: 17323933 DOI: 10.1021/bi602458m] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The mechanism of the oxidative cyclization reaction catalyzed by clavaminic acid synthase (CAS) was studied in silico. First, a classical molecular dynamics (MD) simulation was performed to obtain a realistic structure of the CAS-Fe(IV)=O-succinate-substrate complex; then potential of mean force (PMF) was calculated to assess the feasibility of the beta-lactam ring, more specifically its C4' corner, approaching the oxo atom. Based on the MD structure, a relatively large model of the active site region was selected and used in the B3LYP investigation of the reaction mechanism. The computational results suggest that once the oxoferryl species is formed, the oxidative cyclization catalyzed by CAS most likely involves either a mechanism involving C4'(S)-H bond cleavage of the monocyclic beta-lactam ring, or a biosynthetically unprecedented mechanism comprising (1) oxidation of the hydroxyl group of PCA to an O-radical, (2) retro-aldol-like decomposition of the O-radical to an aldehyde and a C-centered radical, which is stabilized by the captodative effect, (3) abstraction of a hydrogen atom from the C4'(S) position of the C-centered radical by the Fe(III)-OH species yielding an azomethine ylide, and (4) 1,3-dipolar cycloaddition to the ylide with aldehyde acting as a dipolarophile. Precedent for the new proposed mechanism comes from the reported synthesis of oxapenams via 1,3-dipolar cycloaddition reactions of aldehydes and ketones.
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Affiliation(s)
- Tomasz Borowski
- Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239, Cracow, Poland.
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6
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Abstract
The essay examines the evidence upon which the presently accepted version of the mechanism of the cytochrome P450(scc)-catalyzed-cleavage of the sidechain of cholesterol is based. This analysis indicates that the generally held view of the process (two consecutive hydroxylations, followed by cleavage of the resulting glycol) most likely does not describe the true mechanism. The available evidence can not be used to support this traditional notion. Two alternative hypotheses are proposed.
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Affiliation(s)
- S Lieberman
- Department of Obstetrics and Gynecology, Institute for Health Sciences, St. Luke's-Roosevelt Hospital Center, 432W 58th Street, New York, NY 10019, USA.
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Cvrk T, Strobel HW. Photoaffinity labeling of cytochrome P4501A1 with azidocumene: identification of cumene hydroperoxide binding region. Arch Biochem Biophys 1998; 349:95-104. [PMID: 9439587 DOI: 10.1006/abbi.1997.0464] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Cumene hydroperoxide can support cytochrome P450-catalyzed reactions in the absence of molecular oxygen, NADPH, and cytochrome P450-NADPH oxidoreductase. Its binding at the cytochrome P450 active site is governed by the structure of the cumene hydroperoxide binding region. In order to define the region of cytochrome P4501A1 at which cumene hydroperoxide binds, we prepared an analog of cumene hydroperoxide for use as a photoaffinity label. p-Azido-isopro-pylbenzene (azidocumene) and its tritiated derivative were photolyzed in water solution by uv light with a half-life of 29 s. The 7-ethoxycoumarin deethylatation catalyzed by P450 using the cumene hydroperoxide-supported system was strongly inhibited by the presence of the label. Covalent binding to the protein after photoactivation was blocked by 50% in the presence of cumene hydroperoxide. HPLC analysis after trypsin digestion of the labeled protein showed that [3H]-azidocumene was attached covalently to the peptide VDMTPAYGLTLK corresponding to residues 492-503 in the 1A1 sequence. The radioactivity level of this fraction was reduced by 50% when the labeling was carried out in the presence of cumene hydroperoxide. To confirm the identified region the labeled protein was cleaved by cyanogen bromide. HPLC separation of the CNBr digest showed two peaks with a high level of radioactivity. The SDS/Tricine PAGE analysis of the radioactive fraction with an elution time of 43 min revealed a 2.4-kDa peptide carrying a high level of covalently bound radioactivity. The N-terminal sequence identified the labeled peptide to be a fragment generated by CNBr corresponding to residues 494-512. The N-terminal sequence of the labeled peptide with elution time of 27 min, TLKH, matches amino acid residues 501-504 in the P4501A1 sequence. We can conclude that in the overlapping region of all three identified peptides, T501-L502-K503, is the site where azidocumene covalently binds to P4501A1. The sequence alignment of cytochrome P4501A1 with cytochrome P450102 predicts that this region might correspond to beta-sheet structure localized on the distal side of the heme ring near the I helix and the oxygen binding pocket. To our knowledge, this is the first report to localize the cumene hydroperoxide binding region in the cytochrome P450 active site.
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Affiliation(s)
- T Cvrk
- Department of Biochemistry and Molecular Biology, University of Texas Medical School at Houston 77225, USA
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8
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Tipton CL, Shih M, Magat WJ. Isolation and characterization of calmodulin-inactivating cholesterol hydroperoxides. J Lipid Res 1991. [DOI: 10.1016/s0022-2275(20)41907-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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9
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Larroque C, Lange R, Maurin L, Bienvenue A, van Lier JE. On the nature of the cytochrome P450scc "ultimate oxidant": characterization of a productive radical intermediate. Arch Biochem Biophys 1990; 282:198-201. [PMID: 2171430 DOI: 10.1016/0003-9861(90)90104-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The electron paramagnetic (EPR) properties of a transient species detected during a cytochrome P450 (P450)-mediated peroxidative reaction have been compared with those of peroxidases Compound I and model metalloporphyrins. The reaction which was studied with cholesterol-specific P450scc and (20R)-20-hydroperoxycholesterol, occurred without enzyme denaturation. The resulting transient species, which reached its maximum after 50 s reaction, was characterized by a one-line EPR spectrum, g = 2.0035, delta 1/2 = 1.08 mT. The decay of this radical was concomitant with the production of (20R)-20,21-dihydroxycholesterol. The reaction (almost 100% yield) conserved the stereo-specificity of the natural pathway. We suggest this intermediate is a candidate for the in vivo ultimate oxidant in the P450-mediated hydroxylation process. The comparison of the observed EPR spectrum with those of peroxidase Compound I and related synthetic models allows us to propose a FeIV porphyrin II cation radical structure for the intermediate.
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Affiliation(s)
- C Larroque
- Institut National de la Santé et de la Recherche Médicale, Unité 128, Montpellier, France
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10
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Lange R, Maurin L, Larroque C, Bienvenüe A. Interaction of a spin-labelled cholesterol derivative with the cytochrome P-450scc active site. EUROPEAN JOURNAL OF BIOCHEMISTRY 1988; 172:189-95. [PMID: 3345759 DOI: 10.1111/j.1432-1033.1988.tb13872.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The cholesterol analogue 25-doxyl-27-nor-cholesterol (CNO), was found to be a substrate for cytochrome P-450scc. Upon incubation with the cytochrome P-450scc electron transfer system, CNO is transformed to pregnenolone (Km = 33 microM, Vmax = 0.32 min-1). The pregnenolone formation from endogenous cholesterol is strongly inhibited by CNO (50% at 5 microM). It binds tightly to cytochrome P-450scc as evidenced by a reversed type I spectral absorbance change (Kd = 5.9 microM) which is paralleled by a greater hyperfine splitting of the room-temperature CNO ESR spectrum due to an enhanced probe immobilization (Kd = 1.9 microM). This finding is in accord with a rotational correlation time of about 10(-7) s, which is close to the tumbling rate of the protein. At 110 K the CNO-bound cytochrome P-450scc displays the ESR g-values gx = 2.404/2.456, gy = 2.245 and gz = 1.916; these are different from those of cholesterol-liganded cytochrome P-450scc and may thus serve as a marker for cytochrome P-450scc. Our data indicate that the stereospecificity of the cytochrome P-450scc side-chain-cleaving activity is not dependent on the nature of the cholesterol side-chain termination (C25 to C27). The substrate binding site is however rather sensitive to a modification of the side chain. The doxyl ring confers a stronger affinity of the substrate to the enzyme. Upon binding it becomes embedded in the protein matrix, and we estimate that its final position is 0.6-1.0 nm from the heme moiety.
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Affiliation(s)
- R Lange
- INSERM U 128, Montpellier, France
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11
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Smith LL, Made Gowda NM, Teng JI. Sterol hydroperoxide metabolism by Salmonella typhimurium. JOURNAL OF STEROID BIOCHEMISTRY 1987; 26:259-64. [PMID: 3550294 DOI: 10.1016/0022-4731(87)90080-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
In order to rationalize multiphasic dose-response data evincing mutagenicity towards Salmonella typhimurium TA1537 for sterol hydroperoxides 3 beta-hydroxy-5 alpha-cholest-6-ene-5-hydroperoxide and 3 beta-hydroxycholest-5-ene-7 alpha-hydroperoxide their metabolism by the bacterial test strain was investigated. The 5 alpha-hydroperoxide was isomerized to the 7 alpha-hydroperoxide and reduced to 5 alpha-cholest-6-ene-3 beta,5-diol; the 7 alpha-hydroperoxide was reduced to cholest-5-ene-3 beta,7 alpha-diol and transformed to 3 beta-hydroxycholest-5-en-7-one. The 3 beta,5 alpha-diol and 3 beta,7 alpha-diol were not interconverted nor was either transformed to the 7-ketone.
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12
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Trzaskos J, Kawata S, Gaylor JL. Microsomal enzymes of cholesterol biosynthesis. Purification of lanosterol 14 alpha-methyl demethylase cytochrome P-450 from hepatic microsomes. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(18)66920-0] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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13
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Larroque C, van Lier JE. Hydroperoxysterols as a probe for the mechanism of cytochrome P-450scc-mediated hydroxylation. Homolytic versus heterolytic oxygen-oxygen bond scission. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(17)36056-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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14
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Abstract
Cytochrome P-450scc is unusual among members of this class of enzymes in showing a high degree of substrate specificity. Features of the cholesterol structure which are particularly important for binding include the 3 beta-hydroxyl, the delta 5-ring configuration, and the side-chain organization in the 20-22 region. Regarding the ring system, binding appears to require planarity and limited size at the 4-5-6 carbons (the A-B ring juncture). In the region of the 3 beta-hydroxyl, a "cleft" in the binding site extends about 4 A beyond the hydroxyl and can accommodate two additional ether-linked carbons. Evidence indicates that an enzyme residue hydrogen-bonds to the oxygen of the 3 beta hydroxyl, providing much of the energy for the initial enzyme-substrate interaction. The cytochrome shows less specificity for the side-chain structure, except in the region of carbons 20-22 where hydroxylation/side-chain cleavage takes place. The binding cleft for the side-chain is limited to approximately the length of the isocaproic group but can accommodate structural variations beyond the 22-position. Evidence indicates that the region near the 20-22 bond is more limited in size, and that an amino acid residue near the heme iron binds strongly and stereospecifically to the 22R-hydroxyl of the cleavage intermediates, 22R-hydroxycholesterol and 20 alpha, 22R-dihydroxycholesterol. The 22R-hydrogen of cholesterol is very close to the heme iron (approximately 3 A), while the 22S-hydrogen is slightly further (about 4 A). The size and bonding properties of the steroid binding/active site suggest a mechanism which accounts for the stereospecificity and sequence of reactions catalyzed by cytochrome P-450scc.
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Interaction of cytochrome P-450 with a hydroperoxide derived from butylated hydroxytoluene. Mechanism of isomerization. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(19)85132-3] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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16
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Abstract
Apart from the broadly used diosgenin and some further natural compounds sterols gained an increasing importance as raw material for the synthesis of steroid drugs. Parallel to the elucidation of the pathways of the enzymatic degradation of sterols technical processes were developed for a specific degradation of the side-chain to useful primary products. A review is given on the present state of this field and the trends to further improvements.
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17
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Prome D, Lacave C, Monsarrat B, David H, Prome JC. Conversion of sterols and triterpenes by mycobacteria. I Formation of progesterone and 1-dehydroprogesterone from Mycobacterium aurum, strain A+. BIOCHIMICA ET BIOPHYSICA ACTA 1983; 753:60-4. [PMID: 6882787 DOI: 10.1016/0005-2760(83)90098-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Side-chain degradation of sterols by bacteria is known to proceed via oxidation of a terminal methyl group followed by a succession of beta-oxidative steps. By this pathway, the pregnane backbone is not produced. However, examination of cholesterol degradation products using a strain of Mycobacterium aurum shows that progesterone and 1-dehydroprogesterone are present at low levels. These pregnane derivatives were identified by gas-liquid chromatography combined with mass spectrometry. This indicates that an alternative pathway for sterol side-chain degradation occurs in bacteria, which could be of great interest for the biological production of corticosteroid precursors.
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Larroque C, van Lier JE. Spectroscopic evidence for the formation of a transient species during cytochrome P-450scc induced hydroperoxysterol-glycol conversions. Biochem Biophys Res Commun 1983; 112:655-62. [PMID: 6847670 DOI: 10.1016/0006-291x(83)91513-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Spectroscopic analysis of the interaction of the epimeric 20-hydroperoxy derivatives of cholesterol with bovine adrenocortical cytochrome P-450scc preparations suggested the formation of a transient species. The intermediate was detected at 4 degrees C and characterized by a minimum at 412 nm in the difference spectrum.
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Sheets JJ, Vickery LE. C-22-substituted steroid derivatives as substrate analogues and inhibitors of cytochrome P-450scc. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(18)33045-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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21
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Larroque C, Van Lier JE. The subzero temperature stabilized oxyferro complex of purified cytochrome P450scc. FEBS Lett 1980; 115:175-7. [PMID: 7398873 DOI: 10.1016/0014-5793(80)81161-6] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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22
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Alsema GJ, Degenhart HJ, Hoogerbrugge J. Side chain cleavage of hydroxylated sterols by bovine adrenal cortex mitochondria: observation of 25-hydroxylase activity during incubation at pH 7.80. JOURNAL OF STEROID BIOCHEMISTRY 1980; 13:539-43. [PMID: 7392630 DOI: 10.1016/0022-4731(80)90210-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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23
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Aringer L, Eneroth P, Nordström L. Side-chain cleavage of 4-cholesten-3-one, 5-cholesten-3 alpha-ol, beta-sitosterol, and related steroids in endocrine tissues from rat and man. JOURNAL OF STEROID BIOCHEMISTRY 1979; 11:1271-85. [PMID: 513749 DOI: 10.1016/0022-4731(79)90196-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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24
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Conran RM, Nickerson PA. Effect of thyroparathyroidectomy (TPX) on the zona reticularis: a quantitative ultrastructural study. Anat Rec (Hoboken) 1979; 194:405-15. [PMID: 475006 DOI: 10.1002/ar.1091940307] [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: 12/15/2022]
Abstract
Atrophy of zona reticularis cells was observed two weeks after surgical thyroparathyroidectomy (TPX). Quantitative morphological techniques for electron microscopy showed significant decreases in the volume of cytoplasm, nucleus, mitochondria, smooth endoplasmic reticulum and lipid droplets in the zona reticularis of TPX rats. In addition, many mitochnodria contained lipid droplets, some of which occupied virtually the entire matrix of mitochondria. The volume per cell of mitochondria with these inclusions increased significantly after TPX. The lipid droplets may well arise from cytoplasmic droplets by increased transport or reduced metabolism of cholesterol, or by direct incorporation of droplets into the mitochondrial matrix. The serum corticosterone level of TPX rats sacrificed under quiescent conditions did not differ significantly from that of controls. Hypothyroidism induced a significant increase in the volume of peroxisomes per cell in TPX animals which may be related to changes in lipid metabolism or transport.
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25
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27
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Van Lier JE, Rousseau J, Langlois R, Fisher GJ. Mechanism of cholesterol side-chain cleavage. II. The enzymic hydroperoxide-glycol rearrangement of the epimeric 20-hydroperxycholesterols in 18O-enriched water. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 487:395-9. [PMID: 861242 DOI: 10.1016/0005-2760(77)90016-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Incubation of 20 alpha-hydroperoxycholesterol (I) and its 20 beta-isomer, 20 beta-hydroperoxy-20 isocholesterol (II) with adrenocortical mitochondrial preparations in the absence of molecular oxygen, in normal and 18O-enriched water, gave 20 alpha, 22R-dihydroxycholesterol (III) from I and 20 beta,21-dihydroxy-20-iso-cholesterol (IV) from II. Mass spectral analysis of the persilylated glycol products III and IV showed no uptake of 18O, indicating that the oxygen atoms of the C20-, C22- and C21-hydroxyl groups originated from the 20-hydroperoxy atomic oxygen complex is the intermediate in the enzymic oxidative reactions of cholesterol side-chain cleavage.
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