共查询到20条相似文献,搜索用时 31 毫秒
1.
H A Sasame M M Ames S D Nelson 《Biochemical and biophysical research communications》1977,78(3):919-926
Microsomes isolated from whole rat brain were found to contain cytochreme P-450 (0.025 to 0.051 nmoles/mg) and NADPH cytochrome reductase activity (26.0 to 55.0 nmoles/mg/min). The oxidation of estradiol to a reactive metabolite that became covalently bound to rat brain microsomal protein was inhibited 63% by an atmosphere of CO:O2 (9:1), indicating the involvement of a cytochrome P-450 oxygenase. In contrast, this atmosphere had no effect on the binding of either the catechol estrogen, 2-hydroxyestradiol, or several catecholamines to rat brain microsomes. An antibody prepared against NADPH cytochrome reductase was found to decrease significantly both the formation of 2-hydroxyestradiol from estradiol by rat brain microsomes and the covalent binding of the catechol estrogen and catecholamines to rat brain microsomal protein. 相似文献
2.
K M Ivanetich I Aronson I D Katz 《Biochemical and biophysical research communications》1977,74(4):1411-1418
In the presence of hepatic microsomes, vinyl chloride produces a ‘type I’ difference spectrum and stimulates carbon monoxide inhibitable NADPH consumption. A comparison of the binding and Michaelis parameters for the interaction of vinyl chloride with uninduced, phenobarbital and 3-methylcholanthrene induced microsomes indicates that the binding and metabolism of vinyl chloride is catalyzed by more than one type P-450 cytochrome, but predominantly by cytochrome P-450. Metabolites of vinyl chloride from this enzyme system decrease the levels of cytochrome P-450 and microsomal heme, but not cytochrome 5 or NADPH-cytochrome reductase . 相似文献
3.
S.D. Nelson J.R. Mitchell E. Dybing H.A. Sasame 《Biochemical and biophysical research communications》1976,70(4):1157-1165
2-Hydroxyestradiol, 2-hydroxyestrone and 2-hydroxy-17α-ethynylestradiol, oxidation products of naturally occurring estrogens and synthetic estrogens in some oral contraceptives were found to be converted by rat liver microsomes to reactive metabolites that become irreversibly bound to microsomal protein. The irreversible binding required microsomes, oxygen and NADPH. The NADPH could be replaced by a xanthine-xanthine oxidase system which is known to generate superoxide anions. The irreversible binding was substantially inhibited by superoxide dismutase, 30% in those incubations containing NADPH and 98% in those incubations containing the xanthine-xanthine oxidase system. Further studies with 2-hydroxyestradiol showed that microsomal cytochrome P-450 was rate limiting in the NADPH-dependent irreversible binding, because the binding was inhibited 62% by an antibody against NADPH-cytochrome reductase and 70% in an atmosphere of CO:O2 (9:1) when compared to an atmosphere of N2:O2 (9:1). Phenobarbital, a known inducer of cytochrome P-450, had no effect on the irreversible binding of 2-hydroxyestradiol, whereas another inducer of P-450, pregnenolone-16α-carbonitrile, markedly increased the irreversible binding. In contrast, cobaltous chloride, an inhibitor of the synthesis of cytochrome P-450, decreased both P-450 and the irreversible binding. These results are consistent with a mechanism for irreversible binding of estrogens and 2-hydroxyestrogens to microsomes that requires oxidation of the catechol nucleus by cytochrome P-450-generated superoxide anion. 相似文献
4.
The effect of pretreatment with phenobarbitone, rifampicin, β-naphthoflavone, antipyrine and spironolactone on the irreversible binding of ethynyloestradiol to guinea pig liver microsomes has been examined and the corresponding changes in microsomal P-450 content and cytochrome reductase activity measured. Rifampicin produced the greatest increase (220%) in irreversible binding while phenobarbitone produced the greatest increase in both microsomal P-450 content (172%) and cytochrome reductase activity (210%). There was no correlation of irreversible binding with either microsomal P-450 content or with cytochrome reductase activity. 相似文献
5.
H A Sasame J R Gillette M R Boyd 《Biochemical and biophysical research communications》1978,84(2):389-395
An antibody prepared against purified rat liver NADPH-cytochrome reductase inhibited both the pulmonary and hepatic microsomal covalent binding of 4-ipomeanol as well as the respective NADPH-cytochrome reductase activities, findings which are consistent with previous studies which indicated the participation of cytochrome P450 in the metabolic activation of the toxin. An antibody prepared against purified rat liver cytochrome b5, which strongly inhibited both the rat hepatic and pulmonary NADH-dependent cytochrome reductases, and was inactive against the respective NADPH-dependent cytochrome reductases, had little effect on metabolic activation of 4-ipomeanol by hepatic microsomes, but strongly inhibited both the NADH-supported and the NADPH-supported pulmonary microsomal metabolism and covalent binding of the compound. These results suggest that metabolic activation of 4-ipomeanol involves a two-electron transfer in which transfer of the second electron via cytochrome b5 is rate-limiting in lung microsomes. 相似文献
6.
Bengt Jernström Jorge Capdevila Sten Jakobsson Sten Orrenius 《Biochemical and biophysical research communications》1975,64(3):814-822
Cytochrome P-450 from rat lung microsomes has been solubilized and purified 8-fold by using affinity chromatography on an ω-amino--octyl derivative of Sepharose 4B. The purified fraction was free of cytochrome 5 and NADPH-cytochrome reductase and showed spectral characteristics similar to those of lung microsomal cytochrome P-450. When combined with NADPH-cytochrome reductase partially purified from liver microsomes, the cytochrome P-450 fraction supported the hydroxylation of benzo (α)pyrene and the activity was proportional to the content of the hemoprotein. No absolute requirement for phosphatidylcholine was found. 相似文献
7.
NADPH-dependent reductase solubilized from microsomes by peroxidation and its activity 总被引:1,自引:0,他引:1
Johan Högberg Robert E. Larson Annika Kristoferson Sten Orrenius 《Biochemical and biophysical research communications》1974,56(3):836-842
Isolated rat liver microsomes were subjected to enzymatic or non-enzymatic lipid peroxidation . NADPH-dependent cytochrome reductase activity was released from the microsomes into the media during peroxidation. This activity could be recovered from the media by DEAE-cellulose chromatography. The recovered enzyme retained high activity for the reduction of cytochrome and a lower level of activity for the reduction of cytochrome P-450. The active fractions were capable of enzymatically supporting the peroxidation of isolated mitochondria in the presence of organically complexed Fe+3 and NADPH, and in this respect the specific activity was found to be about ten times higher than in microsomes. 相似文献
8.
Both the cytochrome b5 level and NADH cytochrome b5 reductase activity in rat liver microsomes were increased 2-fold by repeated i.p. administration of 1.5 mmol/kg propylthiouracil (PTU) for 2 weeks, but neither the cytochrome P-450 level nor NADPH cytochrome P-450 reductase activity were affected by the treatment. Liver microsomes from PTU-treated rats showed a significant decrease in aminopyrine N-demethylation, but not in benzphetamine N-demethylation, aniline hydroxylation or 7-ethoxycoumarin O-deethylation. A single administration of the compound had no effect on any components of the system. , drug hydroxylation activities were not affected by PTU up to 1.0 mM. From the above evidence, repeated administration of PTU selectively induced cytochrome b5 and NADH cytochrome b5 reductase in rat liver microsomes. 相似文献
9.
Microsomal 11α-hydroxylation of progesterone in : Part I: Characterization of the hydroxylase system
C.R. Jayanthi Prema Madyastha K.Madhava Madyastha 《Biochemical and biophysical research communications》1982,106(4):1262-1268
Microsomes (105,000xg sediment) prepared from induced cells of was found to hydroxylate progesterone to 11α-hydroxyprogesterone (11α-OHP) in high yields (85–90% in 30 min.) in the presence of NADPH and O2. The pH optimum for the hydroxylase was found to be 7.7. However, for the isolation of active microsomes grinding of the mycelium should be carried out at pH 8.3. Metyrapone, carbon monoxide, SKF-525A, p-CMB and N-methyl maleimide inhibited the hydroxylase activity indicating the involvement of cytochrome P-450 system. The inhibition of the hydroxylase by cytochrome and the presence of high levels of NADPH-cytochrome reductase in induced microsomes suggest that the reductase could be one of the components in the hydroxylase system. 相似文献
10.
R.K. Bhatnagar S. Ahmad K.K. Kohli K.G. Mukerji T.A. Venkitasubramanian 《Biochemical and biophysical research communications》1982,104(4):1287-1292
The presence of the components of polysubstrate monooxygenase (PSMO) activity, viz., cytochrome P-450 and NADPH cytochrome P-450 reductase has been established for the first time in the microsomes of . The microsomes were able to metabolize benzphetamine. NADPH cytochrome P-450 reductase, benzphetamine metabolism and aflatoxin production was increased by the presence of phenobarbitone (PB, 2mg/ml) in the medium. These results demonstrate that induction of PSMO activity could be a prerequisite for increased production of aflatoxins, since hydroxylation of intermediates is an obligatory step in aflatoxin biosynthesis. 相似文献
11.
Incubation of R(+)-[14C]pulegone with rat liver microsomes in the presence of NADPH resulted in covalent binding of radioactive material to macromolecules. Covalent binding was much higher in phenobarbital-treated microsomes as compared to 3-methylcholanthrene treated or control microsomes. The Km and Vmax of covalent binding was 0.4 mM and 1.7 nmol min-1 mg-1, respectively. Covalent binding was drastically inhibited (93%) in the presence of piperonyl butoxide. Antibodies to phenobarbital-induced cytochrome P-450 and NADPH-cytochrome P-450 reductase inhibited covalent binding to an extent of 72% and 47%, respectively. Cysteine and semicarbazide also inhibited NADPH dependent binding of radiolabel from R(+)-[14C]pulegone to microsomal proteins. The results suggest the involvement of liver microsomal cytochrome P-450 in the bioactivation of R(+)-pulegone to reactive metabolite(s) which might be responsible for covalent binding to macromolecules resulting in toxicity. 相似文献
12.
Bruce A. Mico Richard V. Branchflower Lance R. Pohl Andrew T. Pudzianowski Gilda H. Loew 《Life sciences》1982,30(2):131-137
In order to determine whether CCl4, CBrCl3, CBr4 or CHCl3 undergo oxidative metabolism to electrophilic halogens by liver microsomes, they were incubated with liver microsomes from phenobartital pretreated rats in the presence of NADPH and 2,6-dimethylphenol. The analysis of the reaction mixtures by capillary gas chromatography mass spectrometry revealed that 4-chloro-2,6-dimethylphenol was a metabolite of CCl4 and CBrCl3 whereas 4-bromo-2,6-dimethylphenol was a metabolite of CBr4. The formation of the metabolites was significantly decreased when the reactions were conducted with heat denatured microsomes, in the absence of NADPH or under an atmosphere of N2. These results indicate that the chlorines of CBrCl3 and CCl4 and the bromines of CBr4 are oxidatively metabolized by rat liver microsomes to electrophilic and potentially toxic metabolites. 相似文献
13.
NADPH reduces both liver microsomal cytochrome P-450 and cytochrome . In the presence of CO, ferrous cytochrome P-450 can slowly transfer electrons to amaranth, an azo dye. This reaction is followed by the reoxidation of cytochrome which proceeds at essentially the same rate as does cytochrome P-450 oxidation. It is suggested that cytochrome directly reduces cytochrome P-450 in rat liver microsomes. 相似文献
14.
Highly purified detergent-solubilized NADPH-cytochrome P-450 reductase from phenobarbital-induced rat liver microsomes 总被引:6,自引:0,他引:6
NADPH-cytochrome P-450 reductase was highly purified from liver microsomes of phenobarbital-induced rats by column chromatography on DEAE-cellulose, DEAE-Sephadex A-50, and hydroxylapatite in the presence of deoxycholate or Renex 690, a nonionic detergent. The purified enzyme gave a single major band with a molecular weight of 79,000 daltons on SDS-polyacrylamide gel electrophoresis. FMN and FAD were present in about equal amounts. The most active reductase preparation catalyzed the reduction of 40.9 μmoles of cytochrome per min per mg of protein and, as an indirect measure of cytochrome P-450 reduction, the oxidation of 2.0 μmoles of NADPH per min per mg of protein in a reconstituted hydroxylation system containing benzphetamine as the substrate. 相似文献
15.
Cytochrome P-450 purified to apparent homogeneity from phenobarbital-induced rabbit liver microsomes: catalytic activity and other properties 总被引:3,自引:0,他引:3
T A van der Hoeven D A Haugen M J Coon 《Biochemical and biophysical research communications》1974,60(2):569-575
Cytochrome P-450 was purified to a content of over 17 nmoles per mg of protein from liver microsomes of phenobarbital-treated rabbits by fractionation with polyethylene glycol 6000, DEAE-cellulose column chromatography, and hydroxylapatite column chromatography in the presence of Renex 690, a nonionic detergent. The purified preparation exhibited a single polypeptide band (molecular weight, 49,000 daltons) when submitted to SDS-polyacrylamide gel electrophoresis. Cytochromes P-420 and 5 and NADPH-cytochrome reductase were absent. The reconstituted system containing purified cytochrome P-450, reductase, and phosphatidylcholine catalyzed the hydroxylation of benzphetamine, cyclohexane, aniline, and laurate. 相似文献
16.
Mitsukazu Kitada Chiyo Yamazaki Kouzi Hirota Haruo Kitagawa 《Biochemical and biophysical research communications》1980,93(4):1020-1026
Cytochrome P-450 was purified from phenobarbital-treated guinea pigs to a specific content of 19.8 nmoles per mg of protein, and was free of cytochrome b5 and NADPH-cytochrome reductase. The purified cytochrome P-450 gave a single protein band on sodium dodecylsulfate-polyacrylamide gel electrophoresis, and an apparent molecular weight of about 49,000 was estimated. Benzphetamine N-demethylation activity could be reconstituted by mixing the purified cytochrome, NADPH-cytochrome reductase and phosphatidylcholine. 相似文献
17.
J. F. Ghersi-Egea A. Minn J. L. Daval Z. Jayyosi V. Arnould H. Souhaili-El Amri G. Siest 《Neurochemical research》1989,14(9):883-887
NADPH:cytochrome P-450 (c) reductase is a microsomal enzyme which is involved in the cytochrome P-450-dependent biotransformation of many exogenous agents as well as of some endogenous molecules. Using cytochromec as a substrate, the kinetic parameters of this enzyme were determined in brain microsomes. The comparison of the NADPH:cytochrome P-450 reductase's Vmax values and cytochrome P-450 contents in both fractions, suggests a role of cerebral NADPH:cytochrome P-450 reductase in cytochrome P-450 independent pathways. This is also supported by the different developmental pattern of brain enzyme as compared to the liver enzyme, and by the presence of a relatively high NADPH:cytochrome P-450 reductase activity in immature rat brain and neuronal cultures, while cytochrome P-450 was hardly detectable in these preparations. The enzyme activity was not induced by a phenobarbital chronic treatment neither in the adult brain nor in cultured neurons, suggesting a different regulation of the brain enzyme expression. 相似文献
18.
Reconstituted hamster liver microsomal enzyme system for N-hydroxylation of the carcinogen 2-acetylaminofluorene 总被引:6,自引:0,他引:6
P D Lotlikar L Luha K Zaleski 《Biochemical and biophysical research communications》1974,59(4):1349-1355
A procedure is described for the isolation of cytochrome P-450 fraction from hamster liver microsomes. It involves removal of NADPH-cytochrome c reductase activity by treatment with bacterial protease before solubilization with Triton X-100 and precipitation with ammonium sulfate. Reconstitution studies indicate that 2-acetylaminofluorene -and ring-hydroxylation require both cytochrome P-450 fraction and the reductase fraction. -hydroxylation activity of cytochrome P-450 fraction from 3-methylcholanthrene pretreated hamsters is different and severalfold greater than that of cytochrome P-450 fraction from controls. These results demonstrate for the first time an activation of a chemical carcinogen by a reconstituted cytochrome P-450 enzyme system. 相似文献
19.
The role of cytochrome 5 in the -nitroanisole O-demethylation was studied with a reconstituted system containing a unique cytochrome P-450, isolated from rabbit liver microsomes as a species with a high affinity for cytochrome 5. The maximal activity was obtained in the complete system consisting of cytochrome P-450, NADPH-cytochrome P-450 reductase, NADH-cytochrome 5 reductase, and Triton X-100 in addition to cytochrome 5. The omission of cytochrome 5 from the complete system entirely abolished the activity. These results clearly show that cytochrome 5 is obligatory in the reconstitute p-nitroanisole O-demethylation system, and this cytochrome P-450 probably interacts with cytochrome 5 in such a way that the second electron is transferred from cytochrome 5 and thus exhibits the demethylase activity. 相似文献
20.
Cytochrome P-450 appears to catalyze the formation of phosgene (COCl2) from chloroform (CHCl3) in rat liver microsomes, since this reaction is NADPH dependent and inhibited by carbon monoxide and SKF 525-A. Moreover, the cleavage of the C-H bond appears to be the rate-determining step in this process since deuterium labeled chloroform (CDCl3) is biotransformed into COCl2 slower than is CHCl3. CDCl3 was also less hepatotoxic than CHCl3 suggesting that a similar pathway of metabolism is responsible for the hepatotoxic properties of chloroform. 相似文献