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At least 145 records · Page 8Linked to original sources
PubMed1984

Studies on Tetrahymena microsomal electron transport systems: solubilization of microsomal electron transport enzymes involved in fatty acid desaturation.

Tetrahymena microsomes were solubilized with five different detergents and the effect on electron transport enzymes involved in fatty acid desaturation was studied. Cytochrome b560ms and NADPH-cytochrome c reductase were solubilized with a low concentration detergent (0.25%), in the order of sodium deoxycholate greater than Renex 690 greater than Triton X-100 greater than octylglucoside greater than sodium cholate, whereas all of these detergents at the high concentration (1%) could solubilize preferentially both enzymes (70-100%). Increasing the concentration of various detergents from 0.5 to 1.0% did not produce an incremental change in NADH-ferricyanide reductase solubilization. NADH-cytochrome c reductase system, which would be catalyzed by the cooperation action of NADH-ferricyanide and cytochrome b560ms, was relatively inactivated by all detergents. Compared to the other four detergents, octylglucoside has a much higher recovery of stearoyl-CoA desaturase activities in the supernatant. Our study suggests that octylglucoside may be more useful for the isolation in active form of cyanide-sensitive factor (CSF) from Tetrahymena microsomes.

Animals↗
PubMed1984

Nitrite binding to cytochrome P-450 from liver microsomes of trout (Salmo gairdneri Rich.) and effects on two microsomal enzymes.

Addition of nitrite to dithionite-reduced trout liver microsomes leads to the conversion of cytochrome P-450 into a cytochrome P-420-NO complex, as it does in mammalian microsomes. A loss in cytochrome P-450 and an inhibition of aminopyrine demethylase (AP) activity were observed in vitro at nitrite-concentrations found in the liver of trout exposed in vivo to this toxin. Nitrite had no effect on dimethylaniline monooxygenase (DMA), a cytochrome P-450-independent enzyme.

Aminopyrine N-Demethylase↗
PubMed2001

Binding of microsomal triglyceride transfer protein to lipids results in increased affinity for apolipoprotein B: evidence for stable microsomal MTP-lipid complexes.

Apolipoprotein B (apoB) and microsomal triglyceride transfer protein (MTP) are known to interact with each other. We evaluated the effect of different lipids on the protein-protein interactions between MTP and apoB100 or its C-terminally truncated forms. Negatively charged lipids decreased protein-protein interactions between apoB and MTP. In contrast, zwitterionic phospholipids enhanced (2-4-fold) the binding of apoB100 to MTP by increasing affinity (1.5-3-fold) between these proteins without affecting the number of binding sites. Similarly, phospholipids augmented (1.5-4-fold) the binding of various C-terminally truncated apoB peptides to MTP. The increased binding was greater for apoB peptides containing lipid-binding domains, such as apoB28 and apoB42. Surprisingly, preincubation of apoB28 with lipid vesicles had no effect on MTP binding. In contrast, incubation of MTP with lipid vesicles resulted in a stable association of MTP with vesicles, and MTP-lipid vesicles bound better (5-fold increase) to LDL than did lipid-free MTP. To determine whether MTP exists stably associated with lipids in cells, microsomal contents from COS cells expressing MTP, HepG2 cells, and mouse liver were ultracentrifuged, and MTP was visualized in different density fractions. MTP was found associated and unassociated with lipids. In contrast, apoB17 and apoB:270-570 were present unassociated with lipids in COS cells. These studies show that the binding of MTP to lipids results in increased affinity for apoB and that stable MTP-lipid complexes exist in the lumen of the endoplasmic reticulum. Protein-protein interactions between apoB and MTP may juxtapose lipids associated with MTP to lipid-binding domains of apoB and facilitate hydrophobic interactions leading to enhance affinity. We speculate that MTP-lipid complexes may serve as nuclei to form "primordial lipoproteins" and may also play a role in the bulk addition of lipids during the "core expansion" of these lipoproteins.

Apolipoproteins B↗
PubMed1979

Biochemical studies on the muscle microsomes of Ascaris lumbricoides var. suum. II. Purification and characterization of b-type cytochrome and NADH-ferricyanide reductase from Ascaris muscle microsomes.

A b-type cytochrome and NADH-ferricyanide (FC) reductase were solubilized from Ascaris muscle microsomes by detergents and purified by column chromatography. The purified b-type cytochrome displayed absorption bands at 560 (alpha-peak), 525 (beta-peak), and 424 nm (gamma-peak), with a marked shoulder at 555 nm in the reduced from, 415 nm (gamma-peak) in the oxidized form. This absorption spectrum was different from that of rat liver microsomal cytochrome b5. The molecular weight was estimated to be about 100,000 by SDS-polyacrylamide gel electrophoresis, and the absorption spectrum of alkaline pyridine ferrohemochrome suggested that the prosthetic group of this cytochrome is protoheme. The molecular weight of the purified NADH-FC reductase was estimated to be about 55,000 by SDS-polyacrylamide gel electrophoresis. The purified reductase required NADH as a specific electron donor. The reductase efficiently reduced some redox dyes with NADH, but the reduction of cytochrome c was much slower. The purified reductase, like the membrane-bound reductase, was not inhibited by thiol reagents.

Animals↗
PubMed1982

Dose dependent induction of rat liver microsomal cytochrome P-450 and microsomal enzymatic activities after inhalation of toluene and dichloromethane.

Sprague-Dawley rats were exposed, by inhalation, to toluene and dichloromethane (500, 1,500 or 3,000 p.p.m.) and to benzene (1,500 p.p.m.) for three days. Toluene and benzene increased the concentration of liver microsomal cytochrome P-450. A dose dependent increase in the in vitro liver microsomal formation of several metabolites of biphenyl and benzo(a)pyrene was observed for both dichloromethane and toluene. At the highest dose-level the increase in the vitro formation of benzo(a)pyrene-7,8-dihydrodiol was more than three-fold for both dichloromethane and toluene whereas the formation of benzo(a)pyrene-4,5-dihydrodiol increased more than five-fold following exposure to toluene but less than two-fold after exposure to dichloromethane. Our results suggest that dichloromethane and toluene can modify the metabolism and thereby the toxicity of other environmental contaminants.

Animals↗
PubMed1996

The failure of substrate pKa to influence the microsomal formation of amides from N-benzylamines: the microsomal metabolism of N-benzyl pyrrolidine, N-benzyl carbazole and N-acetyl-N-benzyl-4-methylaniline.

The in-vitro hepatic microsomal metabolism of N-benzylpyrrolidine (NBP), N-benzylcarbazole (NBC) and N-acetyl-N-benzyl-4-methylaniline (NANBMA) has been studied, using hamster microsomal preparations, to establish whether the corresponding amide is formed. Amide formation was not observed with any of the substrates utilized, although several metabolic products were detected by HPLC with UV detection. These included the oxidative debenzylation products (for all substrates), ring hydroxylated products (for NBC) and a lactam metabolite (for NBP). The results support the concept that the metabolic conversion of benzylic amines to the corresponding amide involves an N-oxidative step.

Aniline Compounds↗
PubMed1983

Presentation of benzo(a)pyrene to microsomal enzymes by asbestos fibers in the Salmonella/mammalian microsome mutagenicity test.

The potential effect of asbestos fibers on mutagenicity of benzo(a)pyrene was investigated by using the Ames test. Asbestos fibers without a coating of benzo(a)pyrene or benzo(a)pyrene when not dissolved in DMSO lacked any mutagenic effect in the Salmonella/mammalian microsome mutagenicity test. However, when benzo(a)pyrene was adsorbed onto asbestos, significant numbers of mutated bacteria were observed. This shows that asbestos fibers can serve a carrier role presenting benzo(a)pyrene to the enzymatic microsomal system, thus enhancing mutagenicity of this compound.

Adsorption↗
PubMedDate not supplied

Effect of microsomal enzyme inducers on biliary and urinary excretion of acetaminophen metabolites in rats. Decreased hepatobiliary and increased hepatovascular transport of acetaminophen-glucuronide after microsomal enzyme induction.

Treatment of rats with phenobarbital (PB), 3-methylcholanthrene, and pregnenolone-16 alpha-carbonitrile increased the total (biliary plus urinary) excretion of thioether and glucuronic acid conjugates of acetaminophen (AA) without influencing AA-sulfate excretion, suggesting that these microsomal enzyme inducers enhance both cytochrome P-450-mediated toxication and UDP-glucuronosyltransferase-mediated detoxication of AA. However, induction with transstilbene oxide (TSO) did not increase the total excretion of AA-thioethers or AA-glucuronide and decreased AA-sulfate excretion. In addition, all inducers increased the ratio of AA metabolites excreted into urine over that excreted into bile. The extent of this shift from biliary to urinary excretion was dependent on both the AA metabolite and the inducer. The largest shift in the excretory route was seen with AA-glucuronide and induction with PB and TSO as inducers. Specifically, PB and TSO treatments decreased biliary excretion of AA-glucuronide by 70 and 89%, respectively, and increased its blood concentration up to 6- and 11-fold and urinary excretion 3- and 3.6-fold, respectively. Galactosamine depletes UDP-glucuronic acid from the liver only, thereby inhibiting hepatic but not extrahepatic glucuronidation. Galactosamine treatment prevented the PB-induced increase in AA-glucuronide in blood and urine. This suggests that the PB-induced increases in AA-glucuronide in blood and urine originated from the liver. Thus, microsomal enzyme inducers not only influence xenobiotic biotransformation, but may also after the contribution of the excretory routes (i.e. bile and urine) in the elimination of xenobiotic metabolites by changing the direction of hepatic transport.

Acetaminophen↗
PubMed1990

[Vitamin A and microsomal membranes: the effect of retinol deficiency on lipid microviscosity and phospholipid turnover in rat liver microsomes].

Studies with the use of the fluorescent probe pyrene revealed that vitamin A deficiency in maturing male rats results in the increased microviscosity of liver lipids. This effect seems to be due to changes in the lipid composition of microsomal membranes (increased cholesterol/phospholipid ratio and lowered polyunsaturated fatty acid content) as well as to the low level of retinol. Analysis of microsomal phospholipids labeled with [3H]palmitate and [14C]glycerol revealed that vitamin A deficiency accelerates the turnover of the glycerol skeleton but sharply decelerates that of fatty acid residues. It is concluded that the observed effect of retinol on the structural and functional properties of biological membranes is due to its ability to control the microviscosity and turnover of membrane lipids.

Animals↗
PubMed1985

A possible cyclic AMP-mediated regulation of microsomal fatty acyl-CoA desaturation system in Tetrahymena microsomes.

Profound alterations in the microsomal fatty acyl-CoA desaturase activities and cyclic AMP production of a unicellular eukaryote, Tetrahymena pyriformis NT-1, originally grown in the glucose-deficient medium, were observed, following the administration of glucose or beta-adrenergic agonists such as epinephrine and isoproterenol. There was a great increase of stearoyl-CoA (delta 8) desaturase activity coincident with a 2-fold decrease of oleoyl-CoA (delta 12) desaturase activity over the first 2 h after administration of these compounds. During this period of time, it was found that the production in vivo of labeled oleic acid from [14C]acetic or [3H]palmitic acid increases 2-fold and the formation in vivo of each labeled linoleic and gamma-linolenic acids drastically decreases. Glucose or beta-adrenergic agonists caused an increase of stearoyl-CoA-stimulated reoxidation rate of NADH-reduced cytochrome b5 but depressed oleoyl-CoA-stimulated reoxidation rate of b5, indicating that both desaturase activities are controlled by the respective terminal components of the desaturase system. A significant and reproducible increase of adenylate cyclase activity and a slight decrease of cyclic AMP phosphodiesterase activity were observed to occur within the first 2 h after the addition of these compounds, when cyclic AMP content in Tetrahymena cell rose by 3-4-fold. Propranolol, a beta-adrenergic blocker, abolished the effects of glucose or beta-adrenergic agonists on the activities of fatty acyl-CoA desaturases and the terminal components as well as cyclic AMP production of cells. These results suggest that glucose and beta-adrenergic agonists may modulate the microsomal fatty acyl-CoA desaturase system in Tetrahymena by acting through the increase of intracellular cyclic AMP content.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1985

Microsomal enzymes of cholesterol biosynthesis from lanosterol. Purification and characterization of delta 7-sterol 5-desaturase of rat liver microsomes.

Microsomal delta 7-sterol 5-desaturase of cholesterol biosynthesis is a multienzyme system which catalyzes the introduction of the delta 5-bond into delta 7-cholestenol to form 7-dehydrocholesterol. The detergent-solubilized 5-desaturase has been purified more than 70-fold and resolved from electron carriers and other rat liver microsomal enzymes of sterol biosynthesis by chromatography on DEAE-Sephacel, CM-Sepharose, and immobilized cytochrome b5; the 5-desaturase had not been fully resolved from cytochrom b5 reductase in earlier work. A functional electron transport system for the 5-desaturase has been reconstituted by combining the purified 5-desaturase and electron carriers with egg phosphatidylcholine liposomes. Optimizations of conditions for reconstitution have been obtained; both cytochrome b5 and NADH-cytochrome b5 reductase serve as electron carriers. A pyridine nucleotide-dependent flavoprotein is required and the requirement can be satisfied with either purified cytochrome b5 reductase or cytochrome P-450 reductase. Cyanide and iron-chelators strikingly inhibit the 5-desaturase activity, thus suggesting that 5-desaturase is a metalloenzyme as are other well-characterized cytochrome b5-dependent oxidases. 5-Desaturase is resolved from 4-methyl sterol oxidase activity of cholesterol biosynthesis by chromatography on the immobilized cytochrome b5. This resolution of the two oxidases not only indicates that introduction of the delta 5-bond and oxidation of 4 alpha-methyl groups are catalyzed by different terminal oxidases, but resolution affords enzymes of sufficient purity to carry out reconstitution experiments. A novel assay based on substrate-dependent increments of oxidation of alpha-NADH has been developed for measurement of 5-desaturase activity. Measurement of stoichiometry of 5-desaturase demonstrates that for each equivalent of cis-desaturation of delta 7-cholestenol, 1 eq of NADH is consumed. Along with strict dependence upon oxygen, this observation confirms, as suggested by previous workers, that the 5-desaturation is catalyzed by a mixed function oxidase rather than a dehydrogenase.

Animals↗
PubMed1983

Schistosoma mansoni adult microsomal antigens, a serologic reagent. II. Specificity of antibody responses to the S. mansoni microsomal antigen (MAMA).

The purified Schistosoma mansoni adult microsomal antigen, MAMA, was used in the quantitative single-tube kinetic dependent enzyme-linked immunosorbent assay (k-ELISA) to measure antibody levels of various human patient sera. The 511 serum specimens tested were from patients with both homologous and heterologous infections. Sera from U.S., Egyptian, Brazilian, and Puerto Rican patients infected with S. mansoni reacted strongly with MAMA. Chinese patients infected with S. japonicum, and Nigerians or Egyptians infected with S. haematobium produced much lower responses to this antigen than those infected with S. mansoni. Sera from patients with echinococcosis, filariasis, paragonimiasis, clonorchiasis, trichinosis, amebiasis, and hepatitis and from healthy uninfected control individuals generally contained no detectable antibodies against this antigen. The S. mansoni adult microsomal antigen, MAMA, therefore, appears to be a highly potent and specific reagent for the serodiagnosis of S. mansoni infections.

Animals↗
PubMed1978

Role of phosphatidylcholine on microsomal chain elongation and the fate of stearoyl-CoA in rat liver microsomes.

The effect of phosphatidylcholine dispersion on the chain elongation of palmitoyl-CoA in rat liver microsomes has been investigated. Addition of phosphatidylcholine increased the formation of stearic acid and its incorporation into phosphatidylcholine. In the presence or absence of phosphatidylcholine, newly-formed stearic acid was preferentially incorporated into the C-1 position of phosphatidylcholine. The incorporation of newly formed stearic acid into microsomes was much higher than that into the added phosphatidylcholine dispersion.

Acyl Coenzyme A↗
PubMed1982

[Effect of preincubation of hepatic microsomes in the presence of chloramphenicol on microsomal lipid peroxidation].

The influence of anaerobic preincubation of hepatic microsomes in the presence of chloramphenicol, in the view of reduction of nitro-group has been studied on later peroxidative degradation and activity of several enzymatic systems on lipids of pretreated microsomes. An inhibition of malonaldehyde production and conjugated dienes occurs in these conditions. Activity of methylaniline N-demethylase and Neotetrazolium reductase were not affected. Possible relationships of chloramphenicol and its reduced metabolites on lipoperoxidation are discussed.

Anaerobiosis↗
PubMed1978

Dysregulation of protein synthesis in injured liver. A comparative study on microsomal and cytosole enzyme activities, microsomal lipoperoxidation and polysomal pattern in D-galactosamine and carbon tetrachloride-injured livers.

Despite the presence of a marked decrease in liver protein content 48 h after a single injection of D-galactosamine, increased activities of glucose-6-phosphate dehydrogenase, low-Km hexokinase and pyruvate kinase type M2 were observed in the injured liver. Microsomal aniline hydroxylase activity and cytochrome P-450 content in liver decreased significantly in 48 h of galactosamine treatment but not in the first 2 h in contrast with carbon tetrachloride (CCL4) intoxication. The extents of those changes were not so great as in CCl4-treated rats. The disaggreation of polyribosomes in liver was observed in 24 h of galactosamine treatment. However, the formation of microsomal lipoperoxidation did not increase in the entire course of acute liver injury by the amino sugar. These results taken together with our previous observations indicate that the dysregulation of protein synthesis is an essential biochemical event of hepatocyte injury induced by treatment of rats with galactosamine as well as CCl4.

Animals↗
PubMed1993

[Interrelationship of microsomal and mitochondrial systems for hydroxylating steroids from cattle adrenal cortex: effect of highly-purified components of the mitochondrial monoxygenase system on hydroxylation of steroids by microsomes].

The possibility of functioning of microsomal steroid hydroxylases in the adrenal cortex in the presence of the electron-transporting proteins in mitochondrial monooxygenase systems has been studied. It was found that adrenodoxin reductase stimulates both the 21- and 17 alpha-steroid hydroxylation activities in microsomes of the adrenal cortex with the same efficiency as does NADPH-dependent cytochrome P-450 reductase. Using cytochrome b5 and its specific antibody, an attempt has been made to investigate possible mechanisms of the stimulating effect of adrenodoxin reductase.

Adrenal Glands↗
PubMed1993

Isolation and heterologous expression of cloned cDNAs for two rabbit nasal microsomal proteins, CYP2A10 and CYP2A11, that are related to nasal microsomal cytochrome P450 form a.

Nasal microsomal P450 form a (NMa), a major cytochrome P450 isozyme in rabbit olfactory and respiratory nasal mucosa with high activity toward a variety of odorants and environmental toxicants, was previously purified to electrophoretic homogeneity from rabbit nasal microsomes. In the present study, a cDNA library constructed from poly(A)+ RNA from rabbit respiratory nasal mucosa was screened with antibodies to P450 NMa, and five immunopositive clones were isolated and characterized. Sequence analysis indicated that the clones encode two highly similar P450s that contain 494 amino acid residues, with the first 20 corresponding to P450 NMa, and differ from each other in only 8 residues scattered throughout the polypeptide chains. On the basis of structural homology the two proteins are designated as CYP2A10 and CYP2A11 and are the first members of the P450 2A subfamily to be identified in nasal tissue. Genomic blot analysis indicated that 2A10 and 2A11 are apparently not allelic variants. Both genes are expressed in liver and lung as well as in nasal tissues, as judged by RNA blot analysis, but the relative levels of the two mRNAs differ. Both enzymes were partially purified after expression of the cDNAs in Escherichia coli and shown to catalyze the oxygenation of a variety of substrates, including ethanol and procarcinogens such as N-nitrosodiethylamine and phenacetin. P450 2A10 is generally more active than P450 2A11 and strikingly so in the conversion of testosterone to androstenedione.

Amino Acid Sequence↗
PubMedDate not supplied

Effect of prostaglandin F2 alpha on free radical generation, glutathione content and microsomal oxidase activities in rat liver microsomes induced either by ethanol or acetone.

We studied the effect of prostaglandin F2 alpha on parameters related to microsomal metabolism (free radical production and lipid peroxidation, glutathione content and activity of microsomal oxidases) after an induction by ethanol or acetone combined with starvation. Long-term ethanol administration led to a significant increase in lipid peroxide formation and NADPH-dependent chemiluminescence amplified by luminol and lucigenin. At the same time hydrogen peroxide production and NADPH-stimulated lipid peroxidation were enhanced although the effect did not reach the level of statistical significance. The concentration of reduced glutathione (GSH) in the liver was decreased 2-fold, whereas oxidized glutathione (GSSG) content remained unaltered. Ethanol intoxication resulted in an increase in 7-ethoxycoumarin-O-deethylase (ECOD), 7-benzyloxycoumarin-O-deethylase (BCOD) and 7-ethoxy-resorufin-O-deethylase (EROD) activities, whereas 7-pentoxyresorufin-O-deethylase (PROD) and ethylmorphin-N-demethylase (EMND) activities were unaltered. The combination of acetone treatment with starvation resulted in a significant increase in lipid and hydrogen peroxide formation, NADPH-dependent lipid peroxidation and chemiluminescence. GSH and GSSG concentration in the liver dramatically decreased 5- and 3-fold, respectively. The acetone treatment led to significant increase in EROD, ECOD, BCOD, PROD and EMND activities. The treatment of ethanol-intoxicated rats with prostaglandin F2 alpha (PGF2 alpha) exerted more pronounced prooxidant effect on liver than action of alcohol itself. At the same time, PGF2 alpha improved most of parameters changed by acetone treatment combined with starvation, decreasing lipid peroxide and radical formation and enhancing GSH and GSSG contents.

Acetone↗