Enzyme ingenuity in biological oxidations: a trail leading to cytochrome p450

Cytochrome P450 research and The Journal of Biological Chemistry

In honor of the 100th birthday of Dr. Herbert Tabor, JBC's Editor-in-Chief for 40 years, I will review here JBC's extensive coverage of the field of cytochrome P450 (P450) research. Research on the reactions catalyzed by these enzymes was published in JBC before it was even realized that they were P450s, i.e. they have a "pigment" with an absorption maximum at 450 nm. After the P450 pigment discovery, reported in JBC in 1962, the journal proceeded to publish the methods for measuring P450 activities and many seminal findings. Since then, the P450 field has grown extensively, with significant progress in characterizing these enzymes, including structural features, catalytic mechanisms, regulation, and many other aspects of P450 biochemistry. JBC has been the most influential journal in the P450 field. As with many other research areas, Dr. Tabor deserves a great deal of the credit for significantly advancing this burgeoning and important topic of research.

10-(6'-Plastoquinonyl)decyltriphenylphosphonium (SkQ1) Does Not Increase the Level of Cytochromes P450 in Rat Liver and Human Hepatocyte Cell Culture

Mitochondria-targeted antioxidant SkQ1 did not increase the content of cytochromes P450 in livers of rats that were given SkQ1 in drinking water for 5 days in a dose (2.5 µmol per kg body weight) that exceeded 10 times the SkQ1 therapeutic dose. SkQ1 did not affect the levels of cytochrome P450 forms CYP1A2, CYP2B6, and CYP3A4 in monolayer cultures of freshly isolated human hepatocytes, while specific inducers of these forms (omeprazole, phenobarbital, and rifampicin, respectively) significantly increased expression of the cytochromes P450 under the same conditions. We conclude that therapeutic doses of SkQ1 do not induce cytochromes P450 in liver, and the absence of the inducing effect cannot be explained by poor availability of hepatocytes to SkQ1 in vivo.

Effect of Long-Term Treatment with Antioxidant SkQ1 Added to Drinking Water on Cytochromes P450 Level in Rat Liver

Mitochondria-targeted cationic antioxidant plastoquinonyl decyltriphenylphosphonium (SkQ1) added to drinking water in therapeutic doses (250 nmol/kg per day) for a long time (up to 24 months) does not induce cytochromes P450 in rat liver.

Therapeutic doses of SkQ1 do not induce cytochromes P450 in rat liver

The effect of SkQ1 (a mitochondria-targeted antioxidant) on the level of cytochromes P450 in rat liver was studied. It was found that administration of therapeutic dose of SkQ1 with drinking water for 5 days (250 nmol/kg of body weight per day) did not alter the level of cytochromes P450. Under the same conditions, the standard dose of phenobarbital used for the induction of cytochromes P450 caused the 2.7-fold increase in the content of these cytochromes. We conclude that therapeutic doses of SkQ1 do not induce cytochromes P450 in rats.

Interplay between pro-inflammatory cytokines and brain oxidative stress biomarkers: evidence of parallels between butyl paraben intoxication and the valproic acid brain physiopathology in autism rat model

Butyl paraben is a preservative used in food, drugs and cosmetics. Neurotoxic effect was reported recently beside the potential estrogenic activity of parabens. There is controversy as to the potential harmful effects of butyl parabens, which are suspected to contribute to autism and learning disabilities. The purpose of this study was to examine the similarities between paraben intoxication signs in the rat brain and brain markers in an autistic like rat model. This study provides evidence of many parallels between the two, including (1) oxidative stress, (2) decreased reduced glutathione levels and elevated oxidised glutathione, (3) mitochondrial dysfunction, and (4) neuroinflammation and increased pro-inflammatory cytokine levels in the brain (tumour necrosis factor-alpha, interleukin-1-beta, and interleukin-6). (5) Increased protein oxidation reported by a significant increase in 3-nitrotyrosine (3-NT)/tyrosine ratio. (6) A marked disturbance was found in the production of energy carriers (AMP, ATP and AMP/ATP ratio) in comparison with the control. The evidence suggests that paraben may, to some extent, either cause or contribute to the brain physiopathology in ASDs or pathogens that produce the brain pathology observed in the diagnosed rat model of ASD.

Conformational changes near the cytochrome P450 active site upon binding of two different ligands

It is shown that a stable nitroxyl radical, 4-cyano-2,2,6,6-tetramethylpiperidine-1-oxyl, forms a complex with cytochrome P4502B4 by analogy with the second type substrates by joining directly to pentacoordinate heme iron. The bound radical is inaccessible to water-soluble paramagnetic ions, which confirms its localization in a hydrophobic pocket near the heme. Benzphetamine and N,N-dimethylaniline, the first-type nonpolar substrates, induce conformational changes of the spin-labeled hemoprotein which are evidently accompanied by an increase in the volume of the pocket resulting in emergence of contact with aqueous phase, and the heme-bound spin label becomes accessible to water-soluble paramagnetics. In this case potassium ferricyanide broadens the spin-labeled cytochrome signal and, as a result, lowers the amplitudes of the spectral components. Similar changes were registered at non-micellar concentrations of nonionic detergent Emulgen 913, whose activating effect on hydroxylation reactions is associated, as we showed previously, with its presence in the CYP2B4 active site simultaneously with substrates.

Cytochrome P450 4F subfamily: at the crossroads of eicosanoid and drug metabolism

The cytochrome P450 4F (CYP4F) subfamily has over the last few years come to be recognized for its dual role in modulating the concentrations of eicosanoids during inflammation as well as in the metabolism of clinically significant drugs. The first CYP4F was identified because it catalyzed the hydroxylation of leukotriene B(4) (LTB(4)) and since then many additional members of this subfamily have been documented for their distinct catalytic roles and functional significance. Recent evidence emerging in relation to the temporal change of CYP4F expression in response to injury and infection supports an important function for these isozymes in curtailing inflammation. Their tissue-dependent expression, isoform-based catalytic competence and unique response to the external stimuli imply a critical role for them to regulate organ-specific functions. From this standpoint variations in relative CYP4F levels in humans may have direct influence on the metabolic outcome through their ability to generate and/or degrade bioactive eicosanoids or therapeutic agents. This review covers the enzymatic characteristics and regulatory properties of human and rodent CYP4F isoforms and their physiological relevance to major pathways in eicosanoid and drug metabolism.

Phenomenon of Activation of Cytochrome P450 by Nonionic Detergents

Mechanism of substitution of nonionic detergent Emulgen 913 for phospholipid as an activator of N-demethylase activity of cytochrome P450 form 2B4 (LM2) has been studied. It is shown that such an activation takes place at the detergent concentrations below values critical for micelle formation. Under these conditions, Emulgen does not affect the hexameric state of the cytochrome. The stimulating effect proved to be similar in reconstituted monooxygenase systems containing (a) cytochrome P450 2B4 and NADPH-cytochrome P-450 reductase and (b) cytochrome 2B4 and organic hydroperoxides. These results indicate that the activation is due to an effect of the detergent upon P450 2B4 per se rather than upon P450/flavoprotein complex formation. The above conclusion is supported by the sedimentation data and measurement of the CD spectra of cytochrome P450 2B4 at 380–450 nm.

Omega Oxygenases: Nonheme-iron enzymes and P450 cytochromes

Enzymes that effect with ease one of the most difficult chemical reactions, hydroxylation of an unfunctionalized alkyl group, are of particular interest because highly reactive intermediates must be produced. A typical example, the hydroxylation of fatty acids in the omega position, is now known to occur widely in nature. The catalysts, which can be called "omega-oxygenases," also insert molecular oxygen into a variety of other substrates at positions removed from activating functional groups, as in steroids, eicosanoids, and numerous drugs and other xenobiotics. Progress in the characterization of bacterial nonheme-iron enzymes, and plant, bacterial, and mammalian P450 cytochromes that catalyze fatty acid omega-oxidation, and evidence for multiple functional oxidants are summarized.

CYTOCHROME P450: Nature's Most Versatile Biological Catalyst

The author describes studies that led to the resolution and reconstitution of the cytochrome P450 enzyme system in microsomal membranes. The review indicates how purification and characterization of the cytochromes led to rigorous evidence for multiple isoforms of the oxygenases with distinct chemical and physical properties and different but somewhat overlapping substrate specificities. Present knowledge of the individual steps in the P450 and reductase reaction cycles is summarized, including evidence for the generation of multiple functional oxidants that may contribute to the exceptional diversity of the reactions catalyzed.

JUD COON: 35 YEARS OF P450 RESEARCH, A SYNOPSIS OF P450 HISTORY

The year 2004 marks the 50th anniversary of the discovery of cytochrome P450. Minor J. (Jud) Coon has been a leader in this field for the last 35 years. This review summarizes his contributions to P450 research by discussing six of his most significant publications; not surprisingly, these papers serve as landmarks for the major directions followed in P450 research.