1. 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.2. 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.3. 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.
In the present studies, a novel form of highly purified cytochrome P-450 (cytochrome P-452) isolated from the hepatic microsomes of clofibrate-pretreated rats has been compared to the major isozymes isolated from the hepatic microsomes of rats pretreated with phenobarbital (cytochrome P-450) and 2-naphthoflavone (cytochrome P-447) using a number of biochemical criteria. The results show that these three isozymes exhibit marked structural differences from each other as judged by a complete lack of immunochemical cross-reactivity between the isozymes and the heterologous rabbit serum antibodies using Ouchterlony double diffusion, and non-identity between the limited proteolytic digestion maps of the three isozymes obtained in the presence of chymotrypsin, papain and Staphylococcus aureus V8 proteases. Furthermore, the three isozymes exhibited clear differences in their monomeric molecular weights determined on calibrated sodium dodecyl sulphate/polyacrylamide gel electrophoresis in gels of varying acrylamide concentration. Substantial differences were also observed in the substrate specificities of the isozymes, which were reflected in differences in the turnover rates and positional selectivities of the hemoproteins for some model substrates. In addition, the isozymes differed in their substrate binding affinities and their ability to interact with purified hepatic microsomal cytochrome b5, as judged using difference spectrophotometry. Finally, subtle differences were detected in the ultraviolet visible absorbance spectra of the hemoproteins in the ferric, ferrous, and carbonmonoxyferrous states. Taken collectively, the above data provides compelling evidence that fundamental differences exist between these cytochrome P-450 isozymes, further establishing the uniqueness of the major form of cytochrome P-450 induced by clofibrate pretreatment.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTemperature-dependent spin equilibrium of microsomal and solubilized cytochrome P-450 from rat liverDominick L. Cinti, Stephen G. Sligar, G. Gordon Gibson, and John B. SchenkmanCite this: Biochemistry 1979, 18, 1, 36–42Publication Date (Print):January 1, 1979Publication History Published online1 May 2002Published inissue 1 January 1979https://pubs.acs.org/doi/10.1021/bi00568a006https://doi.org/10.1021/bi00568a006research-articleACS PublicationsRequest reuse permissionsArticle Views49Altmetric-Citations52LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
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