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

Liver endoplasmic membrane contains two hemoproteins, cyt. P-450 and cyt. b5. Cytochrome P-450 catalyzes the hydroxylation of lipid-soluble compounds, while the cyt. b5 system is involved in desaturation of fatty acids. NAD(P)H and oxygen are essential components for both systems. Oxidation of ethanol to acetate in the liver, via alcohol and acetaldehyde dehydrogenases, leads to an elevated cellular NADH content. It has been proposed that oxidation of the cytosolic NADH occurs predominantly in the mitochondria via the substrate oxidation-reduction shuttle. In order to investigate the effects of elevated levels of cytosolic NADH on the state of the endoplasmic hemoprotein system, microsomes from a fatty human liver (post-ethanol intake) were isolated and studied. Microsomal cyt. b5 reductase was found to reoxidize cytoplasmic NADH directly and transfer the reducing equivalents readily to the microsomal oxidases. Addition of catalytic amounts of alcohol dehydrogenase, NAD, and ethanol to microsomes resulted in a rapid reduction of microsomal cyt. b5. These results are consistent with the proposal that the catalytic moiety of cyt. b5 reductase is exposed to the aqueous phase of the membrane and directly accepts reducing equivalents from the cytoplasm. Microsomes from fatty human liver showed an increased rate of cyt. b5 dependent desaturation of fatty acids. These findings suggest that ethanol metabolism may selectively affect the activity of one or the other microsomal hemoprotein. Thus, when the desaturase activity is low, drug metabolism by the cyt. P-450 pathway may predominate. Conversely, an increase in the desaturase level may lead to a decreased drug metabolism. This mechanism may underlie the clinical observations of drug intolerance reactions associated with alcohol intake.
 ...
PMID:The role of microsomal cytochrome b5 in the metabolism of ethanol, drugs and the desaturation of fatty acids. 1 14

Cytochrome P-450 and NADPH-cytochrome P-450 REDUctase, both purified from liver microsomes of phenobarbital-pretreated rabbits, have been incorporated into the membrane of phosphoaditylcholine vesicles by the cholate dialysis method. The reduction of cytochrome P-450 by NADPH in this system is biphasic, consisting of two first-order reactions. The rate constant of the fast phase, in which 80--90% of the total cytochrome is reduced, increases as the molar ratio of the reductase to the cytochrome is increased at a fixed ratio of the cytochrome to phosphatidylcholine, suggesting that the rate-limiting step of the fast phase is the interaction between the reductase and the cytochrome. The rate constant of the fast phase also increases when the amount of phosphatidylcholine, relative to those of the two proteins, is decreased. This latter observation suggests that the interaction between the two proteins is effected by their random collision caused by their lateral mobilities on the plane of the membrane of phosphatidylcholine vesicles. The rate constant of the slow phase as well as the fraction of cytochrome P-450 reducible in the slow phase, on the other hand, remains essentially constant even upon alteration in the ratio of the reductase to the cytochrome or in that of the two proteins to phosphatidylcholine. No satisfactory explanation is as yet available for the cause of the slow-phase reduction of cytochrome P-450. The overall activity of benzphetamine N-demethylation catalyzed by the reconstituted vesicles responds to changes in the composition of the sysTEM IN A SIMILAR WAY TO THE FAST-PHASE REDUCTION OF CYTOCHROME P-450, though the latter is not the rate-limiting step of the overall reaction.
 ...
PMID:Interaction between NADPH-cytochrome P-450 reductase and cytochrome P-450 in the membrane of phosphatidylcholine vesicles. 10 85

It has been demonstrated that the enzyme system of Candida guilliermondii responsible for hydrocarbon oxidation involves NADPH-cytochrome c-reductase (EC 1623) and cytochrome P-450. The system is located in the microsomal fraction. Cytochrome P-450 synthesis is induced by hexadecane occurring in the medium. The cellular content of cytochrome P-450 varies in the course of the culture growth. There is a correlation between the cellular content of cytochrome P-450 and the synthesis of primary products of hexadecane oxidation.
 ...
PMID:[Paraffin oxidizing system of the yeast Candida guilliermondii]. 11 61

Cytochrome P-450 has been purified from liver microsomes of phenobarbital-induced rabbits in the presence of ionic and nonionic detergents to concentrations over 17 nmoles per mg of protein. The purified cytochrome P-450 LM gives a single major band on SDS-polyacrylamide gel electrophoresis representing about 90 per cent of the total protein. The polypeptide chain has a molecular weight of about 49,000 daltons. NADPH-cytochrome P-450 reductase has been purified from liver microsomes of phenobarbital-induced rats in the presence of ionic and nonionic detergents to a stage where it catalyzes the reduction of 33,000 nmoles of cytochrome c per min per mg of protein. The ratio of activities toward cytochrome P-450 and cytochrome c is constant throughout purification. The purified reductase contains equimolar amounts of FMN and FAD and gives a single major band on SDA-polyacrylamide gel electrophoresis accounting for about 70 per cent of the total protein; the molecular weight is about 80,000 daltons. The purified cytochrome P-450 is free of cytochrome b5 but contains another electron acceptor, provisionally called Factor C, which is equivalent in amount to the heme present. Two electrons are taken up per molecule of cytochrome P-450 from dithionite or from NADPH in the presence of catalytic amounts of the reductase, and both electrons are readily transferred from the reduced cytochrome P-450 to molecular oxygen or artificial electron acceptors. The reconstituted enzyme system containing purified cytochrome P-450, purified NADPH-cytochrome P-450 reductase, and phosphatidylcholine retains the ability to catalyze the hydroxylation of drugs, fatty acids, hydrocarbons, and aniline in the presence of NADPH and molecular oxygen.
 ...
PMID:Biochemical characterization of highly purified cytochrome P-450 and other components of the mixed function oxidase system of liver microsomal membranes. 16 50

Cytochrome P-450 was purified from bovine adrenal cortex mitochondria by affinity chromatography using an octylamine-substituted Sepharose column. The resulting optically clear preparation was stable at -20 degrees for months. The specific concentration of cytochrome P-450 in the preparation was about 5 nmol of heme per mg of protein. The preparations were free of adrenodoxin, adrenodoxin reductase, phospholipids, and other heme contaminations. Polyacrylamide gel electrophoresis of the purified cytochrome P-450 preparation treated with sodium dodecyl sulfate and mercaptoethanol showed a single major band with a molecular weight of about 60,000. The optical absorption spectra of the preparation exhibited Soret maxima at 416, 416, and 448 nm for the Fe3+, Fe2+ and the C.Fe2+ complex, respectively. The EPR spectrum showed the characteristic features of the low spin form of ferric cytochrome P-450 with principal components 1.914, 2.241, and 2.415 of the g-tensor. The circular dichroism spectrum revealed two large negative ellipticities at 412 and 350 nm. Fluorescence spectra showed an excitation maximum at 285 nm and an emission maximum at 305 nm with a shoulder at 330 nm as the cytochrome P-450 molecule is excited at 285 nm, or an emission maximum at 335 nm when the cytochrome molecule is excited at 305 nm. After reconstitution with adrenodoxin and its reductase, this cytochrome P-450 was highly active for cholesterol desmolase with an NADPH-generating system as electron donor but was not active for steroid 11beta-hydroxylase.
 ...
PMID:Purification and characterization of adrenal cortex mitochondrial cytochrome P-450 specific for cholesterol side chain cleavage activity. 18 90

The concentrations of cytochrome P-450 and the activities of aryl hydrocarbon [benzo(a)pyrene] hydroxylase (AHH) and reduced nicotinamide adenine dinucleotide phosphate-cytochrome c reductase were measured in early (gray-white) and remodeled (brown) hyperplastic nodules induced in the livers of rats with 2-acetylaminofluorene and were compared to the values in control livers and in the liver surrounding the nodules. Cytochrome P-450 content of early (14 weeks) hyperplastic nodules is 30% of the activity of untreated control livers and 48% of the activity of the surrounding liver. AHH activity of the early nodules is 10% of the control activity and 33% of the activity in the surrounding nonnodular liver. Nicotinamide adenine dinucleotide phosphate-cytochrome c reductase activity in the microsomes of early nodules is 76% of the control activity and 78% of the activity in the surrounding liver. In the late remodeled nodules, (22 and 25 weeks), the cytochrome P-450 content is 40% of that of controls and AHH activity is 15% of the control activity. In primary hepatomas induced by 2-acetylaminofluorene, cytochrome P-450 content is 21% of that of controls, AHH activity is 11% of the activity of controls, and reductase is 50% of the control activity. These results, indicating a relative nodule deficiency in some of the cellular components believed to be important in the activation of hepatocarcinogens and hepatotoxins, offer one possible explanation for the relative resistance to carcinogen cytotoxicity of hyperplastic liver nodules.
 ...
PMID:A relative deficiency of cytochrome P-450 and aryl hydrocarbon [benzo(a)pyrene] hydroxylase in hyperplastic nodules induced by 2-acetylaminofluorene in rat liver. 18 17

Housefly microsomes contain two spectrally different forms of cytochrome P-450 which we have termed P-450 and P-450I. Methods have been developed for the fractionation and chromatographic purification of these two hemoprotein forms. Microsomes are solubilized first with Triton X-100 in the presence of glycerol, dithiothreitol, ethylenediaminetetra-acetic acid, and phenobarbital. Cytochrome P-450 is recovered in a floating pellet after the addition of 25% ammonium sulfate followed by centrifugation, whereas cytochrome P-450I remains in the 25% ammonium sulfate supernatant fluid. Cytochrome P-450 is purified further by Sephadez G-200 and DEAE-Sephadex A-50 column chromatography, which also allows the isolation of cytochrome b5 and NADPH-dependent cytochrome P-450 reductase in good yields and with little cross-contamination. Cytochrome P-450 apparently is free of cytochromes b5 and P-420 as well as of reductase and is obtained in a final yield of approximately 16% with a 6.9-fold purification. Its maximum absorbance is at 45 mn in the CO-difference spectrum and its average extinction coefficient is 103 cm-1 nm-1. Cytochrome P-450I is purified by Sephadex G-25 column chromatography but still contains some cytochromes b5 and P-420 as well as reductase. Its maximum absorbance is at 448.5 nm in the CO-difference spectrum and its extinction coefficient is 83 to 86 cm-1 mM-1. Both cytochromes hydroxylate type I substrates such as aminopyrine. Sufficient amounts of reductase are present in the cytochrome P-450I preparation to sustain activity, but the reductase has to be added to cytochrome P-450 in a reconstituted system for activity. Cytochrome P-450 is fairly stable, whereas cytochrome P-450I can be isolated only when protected by a substrate (phenobarbital). Detergent-solubilized housefly cytochromes P-450 and P-450I seem to correspond to either aggregates or oligomeric proteins. Cytochrome P-450 appears to correspond to a tetramer, each subunit having a molecular weight of 45,000, whereas cytochrome P-450I may correspond to an aggregate of at least 10 subunits. The cytochrome P-450 aggregate is dissociated by 6 M urea, but cytochrome P-450I remains as such.
 ...
PMID:Soluble cytochrome P-450 from housefly microsomes. Partial purification and characterization of two hemoprotein forms. 23 39

Cytochrome P-450 destruction kinetics by cumene hydroperoxide (CHP) has been studied at 25 degrees C in phosphate buffer, pH 7.25-7.50, in various systems: intact and induced rat or rabbit microsomes, highly purified LM2- and LM2- and LM4-forms of cytochrome P-450 from rabbit liver microsomes. The destruction kinetics is characterized by three phases in all systems. The CHP-influenced cytochrome P-450 destruction is a radical chain process with linear termination of the chains. The acidic phospholipids, phosphatidylserine and phosphatidylinositol and total microsomal phospholipids containing the acidic lipid components activate cytochrome P-450 in the hydroxylation of aniline and naphthalene by CHP. Phosphatidylcholine and sphingomyelin have no effect upon the cytochrome P-450 activity in the type I and II substrates oxidation by CHP. The phase transitions of the microsomal phospholipids influence the interaction of cytochrome P-450 with its reductase, altering the activation energy of type I substrates oxidation. The type II substrate oxidation is not affected by phase transitions in the full microsomal hydroxylating system.
 ...
PMID:The mechanism of hydroperoxide-dependent reactions with participation of cytochrome P-450. 51 12

The liver microsomal drug-metabolizing enzyme system consists of two protein components, cytochrome P-450 and NADPH-cytochrome c reductase, and a lipid, phosphatidylcholine. Cytochrome P-450 serves as the binding site for oxygen and substrate while the reductase acts as an electron carrier shuttling electrons from NADPH to cytochrome P-450. The phospholipid facilitates the transfer of electrons from NADPH-cytochrome c reductase to cytochrome P-450 but itself is not an electron carrier. Different cytochromes P-450 and P-448 have been purified; the spectral, catalytic, and immunological properties as well as the molecular weight (determined by SDS-gel electrophoresis) of all these hemeproteins differ from one another. The presence of multiple cytochrome P-450s may explain the species, strain, age, tissue, and sex differences as well as the effect of inducers and nutritional status in mammlian drug metabolism.
 ...
PMID:Liver microsomal drug-metabolizing enzyme system: functional components and their properties. 82 57

Cytochrome P-450 2E1 is induced in adult rabbits by treatment with alcohol, imidazole, and a variety of other agents, as shown earlier in this laboratory, but it is not known whether the highly homologous P-450 2E2 is similarly induced. In this study, the effects of imidazole on 2E2 expression were examined in neonatal rabbits, in which 2E1 is not detectable. Treatment of the animals with imidazole on days 8 through 11 after birth caused a 3-fold increase in the content of total P-450 in liver microsomes. In contrast, the microsomal content of cytochrome b5 and NADPH-P450 reductase was not changed. Immunoblot analysis revealed a significant increase in the level of P-450 2E2 (3-fold) as well as 1A1 (> 10-fold) and 1A2 (> 2-fold) in hepatic microsomes from imidazole-treated neonatal rabbits. The rates of microsomal N-demethylation of N-nitrosodimethylamine and O-deethylation of 7-ethoxyresorufin were similarly increased from 1.3 and 0.03 nmol/min/mg protein, respectively, to 5.6 and 0.24 nmol/min/mg protein, respectively, by imidazole treatment. Blot analysis indicated that the levels of 2E2, 1A1, and 1A2 mRNAs are not increased by imidazole treatment and that 2E1 mRNA is not detectable in either untreated or imidazole-treated neonates. The induction of P-450 2E2 was confirmed by NH2-terminal amino acid sequence analysis of immunopurified 2E protein from hepatic microsomes of imidazole-treated neonatal rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Induction of P-450 cytochromes 2E2, 1A1, and 1A2 by imidazole in neonatal rabbits. 136 28


1 2 3 4 5 Next >>