Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q8NEX9 (reductase)
 26,410 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We report on the presence of multiple forms of NADPH-cyt P450 reductase in microsomes from higher plants. This contrasts with the animal cyt P450 monooxygenases, where the numerous cyt P450 isoforms are reduced by a single form of reductase. Three NADPH-cyt c reductases have been resolved from Jerusalem artichoke tuber microsomes by chromatography on Reactive Red Agarose and Concanavalin A-Sepharose. Their molecular weights, determined by sodium dodecylsulfate-gel electrophoresis, are 80,000, 82,000 and 84,000. The three proteins share common epitopes and are dependent upon FMN for catalytic activity. They are highly selective for NADPH as electron donor, and allowed effective reconstitution of trans-cinnamic acid and 3,9-dihydroxypterocarpan 6a-hydroxylase activities with purified cyt P450 fractions from Helianthus tuberosus and Glycine max, respectively. As such, they appear as true isoenzyme forms of NADPH-cyt P-450 reductase.
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PMID:Multiple forms of NADPH-cytochrome P450 reductase in higher plants. 190 16

Both MPTP and MPP+ inhibited the NADPH-dependent microsomal LPO in mouse brain and lung. On the other hand, PQ significantly stimulated the LPO in brain microsomes in a dose-dependent manner. The herbicide, however, stimulated lung microsomal LPO only in a narrow concentration range, despite much higher P450 reductase activity in lung microsomes than that in brain microsomes. These findings suggest that the effect of PQ on microsomal LPO is different from those of the analogous neurotoxins, MPTP and MPP+, and is not uniform in brain and lung.
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PMID:Effects of MPTP, MPP+, and paraquat on NADPH-dependent lipid peroxidation in mouse brain and lung microsomes. 190 47

Fluorescence quenching of benzo[a]pyrene (BP) by cytochrome P450c was used to probe this substrate-enzyme binding interaction. Addition of NADPH-cytochrome P450 reductase, an essential electron carrier during P450 catalysis, resulted in increased quenching and thus strengthened binding of BP to P450c. This shows that the role of reductase extends beyond that of an electron transfer agent to influence substrate binding. Fluorescence titration measurements revealed that reductase and P450c formed a complex with an apparent KD of 13.7 +/- 0.9 nM. Reductase had no effect in the presence of an anti-P450c monoclonal antibody which inhibits BP hydroxylation, which suggests that this monoclonal antibody binds P450c near its reductase binding region.
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PMID:A fluorescence study of the interactions of benzo[a]pyrene, cytochrome P450c and NADPH-cytochrome P450 reductase. 190 75

A solid-phase membrane mimetic system, denoted as immobilized artificial membranes (IAM), has been developed and utilized as a novel high-performance liquid chromatography (HPLC) matrix for the first step in the rapid purification of functional membrane proteins. IAM phases consist of monolayers of amphiphilic membrane lipid molecules covalently bonded to a rigid silica particle. These monolayers of lipids have proved remarkably effective for the chromatography of biomolecules. Several cytochrome P450 isozymes, an extremely important family of hydrophobic membrane proteins with a labile heme catalytic center, have been partially purified in functional conformations from rat liver, kidney, and adrenal microsomes on IAM supports. Functionality of purified P450 and P450 reductase has been demonstrated by optical difference spectroscopy, by carbon monoxide binding, and by reconstitution of enzymatic activity in vitro. Other membrane proteins, including rat liver plasma membrane NADH oxidase and ferricyanide oxidoreductase have also been partially purified by IAM HPLC. The methods for purification of these proteins are described.
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PMID:Immobilized artificial membrane chromatography: rapid purification of functional membrane proteins. 190 12

Polyclonal antibodies to components of the rat liver cytochrome P450 system were used to examine the composition and function of the microsomal cytochrome P450-dependent monooxygenase system of human colonic mucosal cells. Anticytochrome P450 reductase antibody gave a strong band of immunocross-reactivity in human colon microsomes at the same molecular weight level as purified cytochrome P450 reductase from rat liver, as well as hepatic microsomes isolated from untreated or phenobarbital-treated rats. These results demonstrate the presence of cytochrome P450 reductase in human colon cells. Similarly, cytochromes P450 IIB1 and IIA1 also appear to be present in Western blots of human colon microsomes. These antibodies, as well as antibodies to reductase and cytochrome b5, inhibit dimethylhydrazine metabolism in human colon microsomes to varying degrees. These data argue for a functional P450-dependent drug metabolism system in colon capable of activating/metabolizing the colon-specific model carcinogen, 1,2-dimethylhydrazine.
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PMID:Characterization of cytochrome P450-dependent dimethylhydrazine metabolism in human colon microsomes. 193 72

Tamoxifen (TXF), a triphenylethylene antiestrogen, is the major therapeutic agent for breast cancer. In rare cases, TXF treatment appears to increase incidence of endometrial cancer. Also in rats, TXF was found to induce hepatocellular carcinoma. Previous studies suggested that metabolism of TXF may contribute to its antiestrogenic and anticancer activity. The current study demonstrates a novel route of TXF metabolism. TXF is metabolized by rat and human liver microsomes into a reactive intermediate (txf*) which binds irreversibly to microsomal proteins. The binding requires NADPH and O2 and is inhibited by CO, inhibitors of P-450, and antibodies to rat NADPH-P450 reductase, indicating catalysis by P450. Phenobarbital treatment of rats markedly increases binding, suggesting the involvement of induced P450s. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins from incubation of [14C] TXF with phenobarbital-treated microsomes exhibits a major radiolabeled zone which corresponds to a molecular weight of approximately 54,000, suggesting binding to a P-450. Cysteine and glutathione inhibited the binding of TXF without significantly affecting P-450-mediated metabolism of TXF, possibly by reacting with txf* or by competing for the same binding sites. Exposure of phenobarbital-treated microsomes and control-microsomes to 50 degrees C for 90 s, which inactivates the flavin-containing monooxygenase (FMO), diminished binding and pH 8.6 enhanced binding. Also, alternate FMO substrates inhibited binding. These findings indicate that P-450 and possibly FMO catalyze the reactions leading to the formation of txf*. However, incubations with single-labeled and dual-radiolabeled tamoxifen or with [14C]TXF-N-oxide demonstrated that monodesmethyl-TXF and TXF-N-oxide, the principal P-450 and FMO-mediated metabolites, respectively, are not on the major route of txf* formation, indicating that txf* could not be an aldehyde derived from tamoxifen nitrone. Thus, though the structure of txf* was not characterized, certain possibilities were excluded. Speculations on the structure of txf* and on its possible pharmacological and toxicological activity are presented.
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PMID:Cytochrome P-450-mediated activation and irreversible binding of the antiestrogen tamoxifen to proteins in rat and human liver: possible involvement of flavin-containing monooxygenases in tamoxifen activation. 193 68

Mutagenicity and carcinogenicity of metronidazole (MT) are imputable to the formation of toxic intermediates, which include radical forms derived from the nitroreductive process. Since dimethylsulfoxide (DMSO), the "universal" solvent, can quench free radicals in vitro, it was suggested that DMSO might protect by scavenging free radical generation in vivo. This study wanted to evaluate if DMSO (given concomitantly or prophylactically) protects against the organospecific mutagenicity of MT in vivo by means of the intrasanguineous host-mediated assay. DMSO used as solvent showed a 20%-30% reduction in the mutation frequencies by MT. Prophylactic administration of DMSO for 3 d caused a suppression of the organospecific mutagenicity. However, some increases in the spontaneous mutation frequency and enhancement of MT mutagenicity in kidney were observed. The protective effect was paralleled by a decrease in NADPH cytochrome c (P450) reductase in liver, kidney, and to a lesser extent in lung microsomes from pretreated mice. Inhibition of mutagenic activity might be related to scavenging of radical species as supported by the lack of tissue specificity and no appreciable changes in specific enzyme activity. However, changes in reductase content in prophylactically pretreated mice can affect the quantitative biotransformation of MT to the proximal mutagen contributing to the observed suppression in mutation frequencies.
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PMID:Dimethylsulfoxide as modifier of the organospecific mutagenicity of metronidazole in mice. 197 30

Cytochrome P450IIE1 (IIE1) is a microsomal xenobiotic-activating enzyme that is inducible not only by various chemical agents but also by fasting and diabetes. Using a rat model that mimics human obesity, we have found that hepatic IIE1 levels are also increased by this common clinical disorder. Liver microsomes from rats made obese by feeding with an energy-dense diet displayed elevated aggregate P450 content (+28%) and enhanced catalytic activities associated with IIE1, including low-Km N-nitrosodimethylamine demethylation (+66%), aniline hydroxylation (+52%), p-nitrophenol hydroxylation (+170%), and acetaminophen-cysteine conjugate formation (+28%). In contrast, obesity had no significant effect on cytochrome b5 content, P450 reductase activity, benzphetamine demethylation, or erythromycin demethylation, with the latter two reactions being linked with rat IIC11 and IIIA1, respectively. The enhancement of IIE1-dependent drug-metabolizing activities noted in liver microsomes from obese rats was paralleled by a similar increase (111%) in hepatic IIE1 protein content in these animals, as assessed on immunoblots developed with anti-hamster IIE1 IgG. Anti-IIE1-inhibitable rates of microsomal p-nitrophenol metabolism, a reaction highly correlated with IIE1 content (r = 0.88, p less than 0.01), were over 3-fold higher in obese rats than in nonobese controls, providing additional evidence for the obesity-related increase of hepatic IIE1. The induction of IIE1 by the pathophysiological condition of obesity may provide a biochemical basis for the increased incidence of occult liver disease and certain cancers noted in obese individuals.
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PMID:Induction of cytochrome P450IIE1 in the obese overfed rat. 200 76

Differences in the pattern of growth hormone (GH) secretion in mature rats (i.e., "continuous" secretion in females versus "pulsatile" secretion in males) are thought to be the underlying cause of sex-dependent differences in a subpopulation of liver microsomal P450 enzymes and steroid 5 alpha-reductase. A new strain of dwarf rats (NIMR/AS) has recently been shown to have low or undetectable levels of circulating GH due to a selective defect in pituitary GH synthesis. We have measured the levels and/or activity of IIA1 (P450a), IIA2 (P450m), IIC11 (P450h), IIC12 (P450i), IIIA2 (a P450p isozyme), and steroid 5 alpha-reductase in liver microsomes from male and female dwarf rats, to test the hypothesis that the expression of these sexually dimorphic enzymes is regulated by GH. In mature rats, the levels of liver microsomal IIA2, IIC11, and IIIA2 were higher in male than in female dwarf rats, whereas the levels of activity of IIA1, IIC12, and steroid 5 alpha-reductase were greater in female than in male dwarf rats. These sex differences resulted from age-related changes in either male dwarf rats (i.e., an increase in IIC11 and IIA2 and a decrease in IIA1) or female dwarf rats (i.e., an increase in IIC12 and 5 alpha-reductase and a decrease in IIIA2). The magnitudes of these sex-dependent, age-related changes were essentially indistinguishable from those observed in normal rats. These unexpected results suggest that GH is not the pituitary factor responsible for regulating the levels of sexually dimorphic, steroid-metabolizing enzymes in rat liver. Alternatively, it is possible that these enzymes are regulated by extremely low levels of GH. In either case, the current model of how steroid-metabolizing enzymes are regulated in rats must be revised to account for the normal sexual differentiation of these enzymes in dwarf rats.
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PMID:Evidence from dwarf rats that growth hormone may not regulate the sexual differentiation of liver cytochrome P450 enzymes and steroid 5 alpha-reductase. 205 2

When I began this review my goal was to present a coherent overview of the biochemistry and regulation of the inducible P450 cytochromes of bacteria. Now, at the end, I wonder if a unified perspective is possible at this time. On the basis of admittedly limited data, bacterial P450 systems seem as different from each other as they are, as a group, from the mammalian P450 cytochromes. The most obvious physical difference between the bacterial monooxygenases and their mammalian counterparts is solubility; with several possible exceptions (69, 70, 76), bacterial P450s are soluble whereas the microsomal and mitochondrial P450s are membrane-associated proteins. In structure and organization, however, the few well-characterized prokaryotic P450-dependent systems vary widely. The three-component arrangement is probably most common but even here variation is apparent. The P450cam putidaredoxin reductase contains only FAD and is quite specific for NADH (35, 39); the P450meg megaredoxin reductase contains only FMN and is specific for NADPH (59, 60). Putitive two-component P450 systems in bacteria have not yet been adequately characterized but the P450oct and P450npd monooxygenases (69, 70, 93) could well be organized in this way. The catalytically self-sufficient P450BM-3 is currently the only single-component P450-dependent monooxygenase known but additional examples of this arrangement may well be found in other bacteria. Paradoxically, P450BM-3 is structurally much more analogous to liver microsomal P450 systems than to any other bacterial P450 monooxygenase characterized to date. Another generally recognized difference between prokaryotic and eukaryotic P450s pertains to function; most known bacterial P450-dependent systems initiate the oxidation of recalcitrant carbon compounds so that the hosts can utilize them as sole carbon sources for growth. Some lower eukaryotes [certain yeasts, for example (134)] also employ P450-dependent systems in this way but, among most fungi as well as in higher eukaryotes, P450 cytochromes are involved in specific pathways of sterol or other lipid syntheses or, as in the mammalian liver microsomal systems, in detoxification reactions.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:P450BM-3 and other inducible bacterial P450 cytochromes: biochemistry and regulation. 206 73


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