scholarly journals Studies on the mechanism of hepatic microsomal N-oxide formation. The role of cytochrome P-450 and mixed-function amine oxidase in the N-oxidation of NN-dimethylaniline

1977 ◽  
Vol 164 (3) ◽  
pp. 487-496 ◽  
Author(s):  
P Hlavica ◽  
M Kehl
Keyword(s):  
Microsomal Fraction ◽  
Amine Oxidase ◽  
The Other ◽  
Rabbit Liver ◽  
Oxide Formation ◽  
Intact Rabbit ◽  
Liver Microsomal Fraction ◽  
Nadph Dehydrogenase ◽  
Cytochrome P 450

Evidence is established for the existence of alternative metabolic routes of N-oxidation of NN-dimethylaniline in rabbit liver microsomal fraction. One pathway involves the participation of two types of cytochrome P-450 with different sensitivities towards heat. Both types may represent distinct haemoprotein species or two physical forms of a single pigment. The other pathway is represented by the mixed-function amine oxidase. The enzyme lacks NADPH dehydrogenase activity and is insensitive to treatment with 2-bromo-4'-nitroacetophenone and steapsin: it catalyses N-oxidation of imipramine, trimethylamine and NN-dimethylaniline in molar proportions considerably different from those of the cytochrome P-450-supported reactions. Cytochrome P-450 is estimated to account for the formation of at least 50-60% of the total NN-dimethylaniline N-oxide formed in the intact rabbit liver microsomal fraction, the remainder arising from the action of the mixed-function amine oxidase.

scholarly journals Role of mixed-function amine oxidase in N-hydroxylation of 2-acetamidofluorene by hamster liver microsomal preparations

1973 ◽  
Vol 136 (4) ◽  
pp. 1137-1140 ◽  
Author(s):  
Prabhakar D. Lotlikar ◽  
Kathleen Wertman ◽  
Leida Luha
Keyword(s):  
Cytochrome C ◽  
Amine Oxidase ◽  
Reductase Activity ◽  
Comparative Data ◽  
Oxide Formation ◽  
Cytochrome C Reductase ◽  
Nadph Cytochrome ◽  
Cytochrome P 450 ◽  
Nadph Cytochrome C Reductase

Pretreatment of hamsters with 3-methylcholanthrene (100mg/kg body wt.) 24h before death did not appreciably change the extent of N-oxide formation when hepatic microsomal preparations were incubated with NN-dimethylaniline as substrate. In contrast, the N-hydroxylation of 2-acetamidofluorene was increased severalfold in hepatic microsomal preparations from pretreated animals. Under these conditions there were no appreciable changes in cytochrome P-450 content and NADPH–cytochrome c reductase activity. On the basis of these comparative data, it is suggested that amine oxidase is not involved in N-hydroxylation of 2-acetamidofluorene.

scholarly journals Oxidation of arylcyclopropanes by rabbit liver cytochrome P-450. Mechanistic implications of a multiple oxidation

1985 ◽  
Vol 232 (1) ◽  
pp. 199-203 ◽  
Author(s):  
C J Suckling ◽  
D C Nonhebel ◽  
L Brown ◽  
K E Suckling ◽  
S Seilman ◽  
...  
Keyword(s):  
Active Site ◽  
Microsomal Fraction ◽  
Cumene Hydroperoxide ◽  
Rabbit Liver ◽  
Microsomal Cytochrome ◽  
Liver Cytochrome ◽  
Liver Microsomal Fraction ◽  
Reconstituted System ◽  
Mechanism Of Oxidation ◽  
Cytochrome P 450

The arylcyclopropanes (cyclopropylarenes) cyclopropylbenzene and diphenylcyclopropane are oxidized by rabbit liver microsomal cytochrome P-450, both by the microsomal fraction and by the purified cytochrome in a reconstituted system. The products formed, principally benzoic acid, are due to an unusual triple oxidation of the substrate, which probably remains attached to the active site during the several steps of the oxidation. Both substrates were found to be inhibitors of the cytochrome P-450-dependent O-de-ethylation of 7-ethoxycoumarin. Model oxidation studies with cumene hydroperoxide as oxidizing agent and rabbit liver microsomal fraction as source of enzyme gave similar products to the microsomal and reconstituted systems. The significance of these results in the mechanism of oxidation catalysed by cytochrome P-450 is discussed.

scholarly journals Loss of haem in rat liver caused by the porphyrogenic agent 2-allyl-2-isopropylacetamide

1971 ◽  
Vol 124 (4) ◽  
pp. 767-777 ◽  
Author(s):  
F. De Matteis
Keyword(s):  
Rat Liver ◽  
Microsomal Fraction ◽  
Direct Evidence ◽  
Gradual Increase ◽  
Rapid Loss ◽  
Metabolizing Enzymes ◽  
Liver Microsomal Fraction ◽  
Green Pigments ◽  
Cytochrome P 450 ◽  
Increased Activity

1. The effect of a single dose of 2-allyl-2-isopropylacetamide on the cytochrome P-450 concentration in rat liver microsomal fraction was studied. The drug caused a rapid loss of cytochrome P-450 followed by a gradual increase to above the normal concentration. 2. The loss of cytochrome P-450 was accompanied by a loss of microsomal haem and by a brown–green discoloration of the microsomal fraction suggesting that a change in the chemical constitution of the lost haem had taken place. Direct evidence for this was obtained by prelabelling the liver haems with radioactive 5-aminolaevulate: the drug caused a loss of radioactivity from the haem with an increase of radioactivity in a fraction containing certain un-identified green pigments. 3. Evidence was obtained by a dual-isotopic procedure that rapidly turning-over haem(s) may be preferentially affected. 4. The loss of cytochrome P-450 as well as the loss of microsomal haem and the discoloration of the microsomal fraction were more intense in animals pretreated with phenobarbitone and were much less evident when compound SKF 525-A (2-diethylaminoethyl 3,3-diphenylpropylacetate) was given before 2-allyl-2-isopropylacetamide, suggesting that the activity of the drug-metabolizing enzymes may be involved in these effects. 5. The relevance of the destruction of liver haem to the increased activity of 5-aminolaevulate synthetase caused by 2-allyl-2-isopropylacetamide is discussed.

scholarly journals The effect of magnesium ions on the diemthylaniline oxidation rate and electron transfer in liver microsomal fraction

1973 ◽  
Vol 136 (2) ◽  
pp. 371-379 ◽  
Author(s):  
A. I. Archakov ◽  
I. I. Karuzina ◽  
I. S. Kokareva ◽  
G. I. Bachmanova
Keyword(s):  
Electron Transfer ◽  
Fluorescence Quantum Yield ◽  
Sharp Increase ◽  
Microsomal Fraction ◽  
Magnesium Ions ◽  
Total Rate ◽  
Nadph Oxidation ◽  
Liver Microsomal Fraction ◽  
Rate Limiting ◽  
Cytochrome P 450

1. Reactions of N-demethylation, p-hydroxylation and N-oxidation of one substrate, i.e. dimethylaniline, have been used to show that the activating effect of Mg2+ takes place only in the first two reactions. 2. An increase in Vmax. of N-demethylation of dimethylaniline is accompanied by an increase in Km. In the p-hydroxylation of dimethylaniline Vmax. increases whereas Km does not change. A comparison of the changes in the Km values of these reactions with the change in Ks shows that in both cases Km does not characterize the affinity of cytochrome P-450 for dimethylaniline. 3. The rate-limiting site of N-demethylation and p-hydroxylation of dimethylaniline, as well as the total rate of NADPH oxidation in the presence of dimethylaniline, is between cytochromes b5 and P-450. Addition of Mg2+ to the incubation medium changes the hydrophobic environment of phosphatidylcholine in the membrane, the process being accompanied by a sharp increase in the fluorescence quantum yield of 8-anilinonaphthalene-1-sulphonate.

scholarly journals Role of Different Forms of Rabbit Liver Microsomal Cytochrome P-450 in Biosynthesis of Bile Acids.

1979 ◽  
Vol 33b ◽  
pp. 611-612
Author(s):  
Ronnie Hansson ◽  
Kjell Wikvall ◽  
Sven Mårdh ◽  
Toshiaki Nishida ◽  
Curt R. Enzell ◽  
...  
Keyword(s):  
Bile Acids ◽  
Rabbit Liver ◽  
Microsomal Cytochrome ◽  
Cytochrome P 450

scholarly journals The effect of ethanol on drug oxidations in vitro and the significance of ethanol–cytochrome P-450 interaction

1973 ◽  
Vol 134 (2) ◽  
pp. 367-375 ◽  
Author(s):  
Dominick L. Cinti ◽  
Robert Grundin ◽  
Sten Orrenius
Keyword(s):  
Microsomal Fraction ◽  
Ethanol Concentration ◽  
Inhibitory Effect ◽  
Type I ◽  
Spectral Change ◽  
High Concentration ◽  
Liver Slices ◽  
Liver Microsomal Fraction ◽  
Cytochrome P 450 ◽  
High Ethanol

The effect of ethanol on N-demethylation of aminopyrine in rat liver slices and in the microsomal fraction and on microsomal hydroxylation of pentobarbital and aniline was studied. With liver slices N-demethylation of aminopyrine was stimulated by 35–40% at low ethanol concentrations (2mm), whereas no stimulation occurred at high concentrations (100mm). With the liver microsomal fraction, an inhibitory effect was observed only at high ethanol concentrations (100mm). This was also observed with the other drugs studied. In agreement with these results, only at a high concentration did ethanol interfere with the binding of drug substrates to cytochrome P-450. Further, as previously reported, ethanol produced a reverse type I spectral change when added to the liver microsomal fraction. Evidence that this spectral change is due to removal of substrate, endogenously bound to cytochrome P-450, is reported. A dual effect of ethanol is assumed to explain the present findings; in liver slices, at a low ethanol concentration, the enhanced rate of drug oxidation is the result of an increased NADH concentration, whereas the inhibitory effect observed with the microsomal fraction at high ethanol concentration is due to the interference by ethanol with the binding of drug substrates to cytochrome P-450.

Cytochrome P-450 from Tulip Bulbs (Tulipa fosteriana L.) Oxidizes an Azo Dye Sudan I (1-Phenylazo-2-hydroxynaphthalene, Solvent Yellow 14) in vitro

1996 ◽  
Vol 61 (11) ◽  
pp. 1689-1696
Author(s):  
Marie Stiborová ◽  
Hana Hansíková
Keyword(s):  
Azo Dye ◽  
Microsomal Fraction ◽  
Point Of View ◽  
Transport Chain ◽  
Sudan I ◽  
Tulip Bulbs ◽  
Metabolism Of Xenobiotics ◽  
Cytochrome P 450

The microsomal fraction from tulip bulbs (Tulipa fosteriana L.) contains cytochrome P-450 enzymes catalyzing the NADPH-dependent oxidation of the xenobiotic substrate, an azo dye Sudan I (1-phenylazo-2-hydroxynaphthalene, Solvent Yellow 14). C-Hydroxy derivatives [1-(4-hydroxyphenylazo)-2-hydroxynaphthalene, 1-phenylazo-2,6-dihydroxynaphthalene, 1-(4-hydroxyphenylazo)-2,6-dihydroxynaphthalene] and the benzenediazonium ion are the products of the Sudan I oxidation. The oxidation of Sudan I has also been assessed in a reconstituted electron-transport chain with the isolated cytochrome P-450, isolated plant NADPH-cytochrome P-450 reductase and phospholipid. The results are discussed from the point of view of the role of cytochromes P-450 in the metabolism of xenobiotics in plants.

scholarly journals Mechanism of inhibition of microsomal mixed-function oxidation by the gut-contents inhibitor of the southern armyworm (Prodenia eridania)

1971 ◽  
Vol 124 (2) ◽  
pp. 427-430 ◽  
Author(s):  
S. Orrenius ◽  
M. Berggren ◽  
P. Moldéus ◽  
R. I. Krieger
Keyword(s):  
Microsomal Fraction ◽  
Gut Contents ◽  
Oxidation Reactions ◽  
Mechanism Of Inhibition ◽  
Southern Armyworm ◽  
Low Concentrations ◽  
Liver Microsomal Fraction ◽  
Cytochrome P 450 ◽  
Nadph Cytochrome C Reductase

A potent inhibitor of microsomal mixed-function oxidation reactions in insects had previously been isolated and partially purified from the gut contents of Prodenia eridania and shown to be associated with proteinase activity. Incubation of rat liver microsomal fraction with low concentrations of this inhibitor led to solubilization of NADPH–cytochrome c reductase, which was paralleled by the inactivation of reduction of cytochrome P-450 by NADPH and by the inhibition of NADPH-linked benzo[3,4]pyrene hydroxylation and aminopyrine demethylation. There was little or no effect on cytochromes b5 and P-450, nor was the capacity of the latter catalyst to combine with exogenous substrates decreased. Contrary to the findings with NADPH, preincubation of microsomal fraction with the inhibitor did not cause a significant decrease in the rate of cytochrome P-450 reduction by NADH, supporting the assumption that different catalysts are involved in the electron transfer from NADH and NADPH to cytochrome P-450. The findings indicate the importance of taking the possible presence of endogenous inhibitors into consideration when evaluating low or absent mixed-function oxidation activities found in insect systems in vitro.

scholarly journals A requirement for dietary lipids for induction of cytochrome P-450 by phenobarbitone in rat liver microsomal fraction

1971 ◽  
Vol 122 (4) ◽  
pp. 569-573 ◽  
Author(s):  
W. J. Marshall ◽  
A. E. M. McLean
Keyword(s):  
Enzyme Activity ◽  
Linoleic Acid ◽  
Dietary Protein ◽  
Microsomal Fraction ◽  
Coconut Oil ◽  
Dietary Lipids ◽  
Liver Microsomal Fraction ◽  
The Difference ◽  
Microsomal Hydroxylation ◽  
Cytochrome P 450

1. Rats fed on purified synthetic diets have a markedly lower cytochrome P-450 concentration and hydroxylating enzyme activity in liver microsomal fraction than rats fed on stock pellets. 2. When both groups are treated with phenobarbitone the difference is even greater, the purified diet allowing only 50% of the cytochrome P-450 concentrations of controls. 3. Addition of herring oil, linoleic acid or 0.1% oxidized sitosterol to the diets allows induction of cytochrome P-450 to take place. 4. Addition of coconut oil to the diet does not permit induction of cytochrome P-450. 5. The interactions between dietary protein and the lipid substances are explored. 6. The mechanism of induction of microsomal hydroxylation enzymes by drugs is discussed in the light of these requirements.

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