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The fluroxene mediated degradation of cytochromes P-450
The degradation of cytochromes P-450 by fluroxene (2,2,2-trifluoroethyl vinyl ether) has been investigated. Fluroxene is shown to specifically degrade cytochromes P-450 in vivo and in vitro without affecting the levels of the other microsomal enzymes, cytochrome ~S a.nd NADPH-cytochrome~ reductase....
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| Format: | Thesis |
| Language: | English |
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Division of Medical Biochemistry
2020
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| _version_ | 1867613272666013696 |
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| access_status_str | Open Access |
| author | Bradshaw, Jennifer Jean |
| author2 | Ivanetich, Kathryn M. |
| author_browse | Bradshaw, Jennifer Jean Ivanetich, Kathryn M. |
| author_facet | Ivanetich, Kathryn M. Bradshaw, Jennifer Jean |
| author_sort | Bradshaw, Jennifer Jean |
| collection | Thesis |
| description | The degradation of cytochromes P-450 by fluroxene (2,2,2-trifluoroethyl vinyl ether) has been investigated. Fluroxene is shown to specifically degrade cytochromes P-450 in vivo and in vitro without affecting the levels of the other microsomal enzymes, cytochrome ~S a.nd NADPH-cytochrome~ reductase. Fluroxene appears to degrade the haem moiety of cytochromes P-450 but does not affect the level of the apoprotein. The degradation of cyto-chromes P-450 by fluroxene is accompanied by a loss of E-nitroanisole 0-demethylase and biphenyl 4-hydroxylase activities and a decrease in the extent of aniline binding is observed. By using cytochromes P-450 dependent reactions which are catalysed by specific type P-450 cytochromes,~.~· the hydroxylation of benzpyrene, the N-demethylation of ethyl-morphine and the binding of ethyl isocyanide, it is established that only cytochrome P-450 is degraded by fluroxene in vivo following phenobarbital induction of animals, and both cytochrome P-450 and cytochrome P-448 following methylcholanthrene induction. The same type P-450 cytochromes are shown to be degraded by fluroxene in vitro in phenobarbital and methylcholanthrene induced microsomes. This was established from studies of the kinetics of the fluroxene mediated degradation of cyto-chromes P-450. In addition, the K values for the flurox-m ene mediated degradation of cytochromes P-450 differ with
iii the different inducing agents and indicate the involve-ment of two different type P-450 cytochromes in the degradation reaction in methylcholanthrene induced micro-somes. Metabolic activation of cytochromes P-450 by the cyto-chromes P-450 drug metabolising pathway appears to be essential for the fluroxene mediated degradation of cyto-chromes P-450. Since none of the known or proposed metabolites of fluroxene can mimic the degradation of cytochromes P-450 by fluroxene, a reactive species is proposed to be involved. By varying the experimental conditions, and with the use of inhibitors of cytochromes P-450, the likely sequence of events in the fluroxene mediated degradation of cytochromes P-450 is shown to be as follows: fluroxene is metabolised by cytochrome P-450 to a transient reactive intermediate which has the ability to degrade the haem moiety of cytochrome P-450 and cyto-chrome P-448. By comparing the ability of various analogues of fluroxene to degrade cytochromes P-450, it is established that the formation of the proposed reactive intermediate is dependent on the presence of the vinyl moiety of the molecule. Initial studies indicate that the reactive species may take the form of an epoxide. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/31857 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:33:31.121Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2020 |
| publishDateRange | 2020 |
| publishDateSort | 2020 |
| publisher | Division of Medical Biochemistry |
| publisherStr | Division of Medical Biochemistry |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/31857 The fluroxene mediated degradation of cytochromes P-450 Bradshaw, Jennifer Jean Ivanetich, Kathryn M. Fluroxene cytochromes P-450 The degradation of cytochromes P-450 by fluroxene (2,2,2-trifluoroethyl vinyl ether) has been investigated. Fluroxene is shown to specifically degrade cytochromes P-450 in vivo and in vitro without affecting the levels of the other microsomal enzymes, cytochrome ~S a.nd NADPH-cytochrome~ reductase. Fluroxene appears to degrade the haem moiety of cytochromes P-450 but does not affect the level of the apoprotein. The degradation of cyto-chromes P-450 by fluroxene is accompanied by a loss of E-nitroanisole 0-demethylase and biphenyl 4-hydroxylase activities and a decrease in the extent of aniline binding is observed. By using cytochromes P-450 dependent reactions which are catalysed by specific type P-450 cytochromes,~.~· the hydroxylation of benzpyrene, the N-demethylation of ethyl-morphine and the binding of ethyl isocyanide, it is established that only cytochrome P-450 is degraded by fluroxene in vivo following phenobarbital induction of animals, and both cytochrome P-450 and cytochrome P-448 following methylcholanthrene induction. The same type P-450 cytochromes are shown to be degraded by fluroxene in vitro in phenobarbital and methylcholanthrene induced microsomes. This was established from studies of the kinetics of the fluroxene mediated degradation of cyto-chromes P-450. In addition, the K values for the flurox-m ene mediated degradation of cytochromes P-450 differ with iii the different inducing agents and indicate the involve-ment of two different type P-450 cytochromes in the degradation reaction in methylcholanthrene induced micro-somes. Metabolic activation of cytochromes P-450 by the cyto-chromes P-450 drug metabolising pathway appears to be essential for the fluroxene mediated degradation of cyto-chromes P-450. Since none of the known or proposed metabolites of fluroxene can mimic the degradation of cytochromes P-450 by fluroxene, a reactive species is proposed to be involved. By varying the experimental conditions, and with the use of inhibitors of cytochromes P-450, the likely sequence of events in the fluroxene mediated degradation of cytochromes P-450 is shown to be as follows: fluroxene is metabolised by cytochrome P-450 to a transient reactive intermediate which has the ability to degrade the haem moiety of cytochrome P-450 and cyto-chrome P-448. By comparing the ability of various analogues of fluroxene to degrade cytochromes P-450, it is established that the formation of the proposed reactive intermediate is dependent on the presence of the vinyl moiety of the molecule. Initial studies indicate that the reactive species may take the form of an epoxide. 2020-05-12T12:16:28Z 2020-05-12T12:16:28Z 1977 2020-04-03T07:40:40Z Master Thesis Masters https://hdl.handle.net/11427/31857 eng application/pdf Division of Medical Biochemistry Faculty of Health Sciences |
| spellingShingle | Fluroxene cytochromes P-450 Bradshaw, Jennifer Jean The fluroxene mediated degradation of cytochromes P-450 |
| thesis_degree_str | Master's |
| title | The fluroxene mediated degradation of cytochromes P-450 |
| title_full | The fluroxene mediated degradation of cytochromes P-450 |
| title_fullStr | The fluroxene mediated degradation of cytochromes P-450 |
| title_full_unstemmed | The fluroxene mediated degradation of cytochromes P-450 |
| title_short | The fluroxene mediated degradation of cytochromes P-450 |
| title_sort | fluroxene mediated degradation of cytochromes p 450 |
| topic | Fluroxene cytochromes P-450 |
| url | https://hdl.handle.net/11427/31857 |
| work_keys_str_mv | AT bradshawjenniferjean thefluroxenemediateddegradationofcytochromesp450 AT bradshawjenniferjean fluroxenemediateddegradationofcytochromesp450 |