Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cytochrome P-450-metabolic intermediate complexes were formed from N-hydroxyamphetamine, benzphetamine, norbenzphetamine, and d- and l-amphetamine in lung microsomal fractions and from N-hydroxyamphetamine in small intestinal mucosa microsomal fractions. Complexes were not formed in either tissue from SKF 525-A or propoxyphene. The rates of metabolic intermediate complex formation, per mole of cytochrome P-450, were higher in lung than in liver or small intestine. In contrast to that in liver, metabolic intermediate complex formation in the extrahepatic tissues was not dramatically affected by phenobarbital or 3-methylcholanthrene treatment.
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PMID:The formation of cytochrome P-450-metabolic intermediate complexes in microsomal fractions from extrahepatic tissues of the rabbit. 1 77

(NADPH)-cytochrome P-450 reductase was purified to apparent homogeneity by a procedure utilizing nicotinamide adenine dinucleotide phosphate (NADP)-Sepharose affinity column chromatography. The purified flavoprotein has a molecular weight of 79 700 and catalyzes cytochrome P-450 dependent drug metabolism, as well as reduction of exogenous electron acceptors. Aerobic titration of cytochrome P-450 reductase with NADPH indicates that an air-stable reduced form of the enzyme is generated by the addition of 0.5 mol of NADPH per mole of flavin, as judged by spectral characteristics. Further addition of NADPH causes no other changes in the absorbance spectrum. A Km value for NADPH of 5 micron was observed when either cytochrome P-450 or cytochrome c was employed as electron acceptor. A Km value of 8 +/- 2 micron was determined for cytochrome c and a Km of 0.09 +/- 0.01 micron was estimated for cytochrome P-450.
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PMID:NADPH-cytochrome P-450 reductase from rat liver: purification by affinity chromatography and characterization. 1 71

The interaction between cytochrome P-450 and NADPH-cytochrome c reductase during catalysis has been investigated with a reconstituted monooxygenase system composed of the two purified enzyme components and synthetic phospholipid. Steady state kinetic data are consistent with a scheme in which the formation of a binary complex between the two proteins precedes catalysis. The formation of this binary complex is described by a simple mass action equation. In agreement with this equation, the observed Vmax for benzphetamine N-demethylation was found to be directly proportional to the calculated concentration of the cytochrome P-450 . reductase complex. Furthermore, with appropriate reductase/cytochrome P-450 mole ratios, the Vmax could be shown to be linearly dependent on either the reductase or the cytochrome P-450 concentration alone. In contrast, the Km parameter is independent of the complex concentration, indicating that no change in the rate-limiting step has occurred. Thus a distinction should be made between a rate-limiting enzyme component and the rate-limiting step in this multienzyme system.
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PMID:Studies on the association of cytochrome P-450 and NADPH-cytochrome c reductase during catalysis in a reconstituted hydroxylating system. 10 41

The chlorinated dibenzo-p-dioxins and dibenzofurans are formed as trace contaminants during the synthesis of a number of commercially important chemicals. The prototype compound of this group, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), is one of the most potent low molecular weight toxins and teratogens known, and its inadvertent dispersion in the environment has caused concern about the potential hazard to human health. In studying the biochemical effects of TCDD, it was found to be extraordinarily potent as an inducer of two hepatic enzymes: 1) delta-aminolevulinic acid synthetase, the initial and rate-limiting enzyme in heme synthesis, and 2) aryl hydrocarbon hydroxylase, a cytochrome P-450-mediated microsomal monooxygenase. Among a series of halogenated dibenzo-p-dioxins there is an excellent correlation between their toxic potency and their potency as inducers of these two enzymes. The administration of polycyclic aromatic hydrocarbons (e.g., 3-methylcholanthrene (MC)) to certain inbred strains of mice induces aryl hydrocarbon hydroxylase, while other inbred strains fail to respond; and the trait of aryl hydrocarbon responsiveness is inherited as an autosomal dominant. TCDD, about 30,000 times as potent as MC, induces all strains whether responsive or nonresponsive to MC; however, the responsive strains are more sensitive (ED 50 approximately 1 X 10(-9) mole/kg) to TCDD than are the nonresponsive strains (ED50 larger than or equal to 1 X 10(-8) mole/kg). The results suggest that the mutation in the nonresponsive strains results in a ligand binding site (an induction receptor) that has a diminished affinity for MC and TCDD. The correlation among the halogenated dibenzo-p-dioxins, between their potency as toxins and their potency as inducers of aryl hydrocarbon hydroxylase, is discussed in relationship to various proposed mechanisms of toxicity.
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PMID:2,3,7,8-Tetrachlorodibenzo-p-dioxin: environmental contaminant and molecular probe. 13 10

The interaction of cytochrome P-450 of rat liver microsomes with six amines have been investigated in Tris-HCL buffer pH 7.4 within the temperature range of 20--37 degrees C by the differential spectrophotometry method. Dissociation constants for the amine-cytochrome-P-450 complexes have been determined. The interaction of type I substrate, 1,2,7-trimethyl-decahydroquinolone-4, is characterized by the value of Ks(I)=4.14 exp (--6250/RT) mole/1. A value of Ks(II)=10(-8) exp (+6500/RT) mole/1 has been obtained for type II substrate, monomethylaniline. Association of 1,2,7-trimethyldecahydroquinolone-4 to cytochrome P-450 decreases with temperature, where as with monomethylaniline the reverse tendency is observed. Thermodynamic parameters delta H, delta F and delta S characterising the interaction of amines with cytochrome P-450 are evaluated.
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PMID:[Effect of temperature on the interaction of cytochrome P-450 with a variety of amines]. 59 14

A cytochrome P-450 from bovine adrenocortical mitochondria has been purified to near homogeneity. The protein catalyzes side-chain cleavage of cholesterol (cholesterol leads to pregnenolone) but neither 11beta- nor 18-hydroxylation. It consists of 16 subunits of two species (MW 52,000) and contains 8 heme groups. The enzyme has been used to determine the stoichiometry of side-chain cleavage with the following results: (TPNH and O2 consumed/mole of cleavage), cholesterol 3:3:1, 20S-hydroxycholesterol 2:2:1 and 20S,22R-dihydroxycholesterol 1:1:1. These findings support the occurrence of the proposed pathway for the side-chain cleavage of cholesterol. Cleavage of the diol is inhibited by CO and shows a characteristic P-450 photochemical action spectrum. Evidently the diol is cleaved in a typical monoxygenase reaction. The active form of the enzyme contains 16 subunits (protein 16); forms consisting of 8 (protein 8) and 4 (protein 4) subunits can be isolated and are enzymatically active only by prior conversion to protein 16.
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PMID:The role of cytochrome P-450 in the regulation of steroid biosynthesis. 96 34

The cytostatic drug dacarbazine [DTIC, 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide] is strongly carcinogenic in rats. Bioactivation of DTIC yields a methylating intermediate but the extent of interaction with cellular macromolecules has not previously been reported. Following a single i.p. injection of [14C-methyl]DTIC, exhalation of 14CO2 occurred with a t1/2 max of approximately 2 hr (0.95 mg/kg) and 2.5 hr (95 mg/kg). Of the total radioactivity administered, 8.5% was exhaled as 14CO2; 54% was excreted via the urine, predominantly as unchanged DTIC. In liver, kidney and lung, formation of 7-[14C]methylguanine in DNA and RNA was directly proportional with dose. DNA methylation by a single dose of DTIC (9.8 mg/kg; 5 hr survival time) was highest in liver (35 mumoles 7-methylguanine/mole guanine), followed by kidney (25 mumoles) and lung (20 mumoles). The remainder tissues showed 7-methylguanine concentrations approximately 50% of those in liver DNA, with the exception of the brain which had a very low extent of DNA modification (approximately 1 mumole/mole guanine). At the specific radioactivity used (48 mCi/mmole), the promutagenic base O6-methylguanine was only detectable in liver, kidney, lung, and stomach DNA (0.6-0.8 mumoles/mole guanine). Autoradiographic studies revealed a diffuse distribution of reaction products in rat liver. In contrast, N-nitrosodimethylamine and related carcinogens known to be bioactivated by the hepatic cytochrome P-450 system show a predominantly centrilobular distribution. This difference may be due to the greater stability of proximate carcinogens generated by alpha-C hydroxylation at one of the methyl groups of DTIC.
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PMID:In vivo metabolism and reaction with DNA of the cytostatic agent, 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide (DTIC). 309 35

We have investigated the nitroreduction of the 2-nitroimidazole benznidazole (BENZO) to its corresponding amine by murine normal tissues and tumours. In vivo concentrations of BENZO and its amine metabolite were measured by HPLC 3 hr after BENZO, 2.5 mmoles kg-1 i.p. This gave plasma and tissue BENZO concentrations of 96-160 micrograms ml-1 or g-1. Mouse plasma, KHT and RIF-1 tumour BENZO amine concentrations were very low (0.3-1.4 micrograms g-1); kidney and EMT6 tumours had intermediate levels; and liver contained very high amine levels (approximately 50 micrograms g-1). Three per cent of the BENZO dose was recovered as amine in the 24 hr urine, compared to 5% for the parent compound. Nitroreduction to the amine was demonstrated with liver and tumour preparations under N2 in vitro. The reaction was highly dependent on NADPH, and inhibited extensively in air. With liver microsomes and whole homogenates 2 and 3 moles respectively of BENZO were consumed per mole of amine formed. Inhibitor studies showed that NADPH: cytochrome P-450 (cytochrome c) reductase and cytochrome P-450 were both involved in BENZO reduction, predominantly at early and late reduction steps respectively. Aldehyde oxidase contributed to the cytosolic nitroreduction. Purified buttermilk xanthine oxidase also reduced BENZO to its amine under anaerobic conditions in vitro, but very inefficiently. The apparent Km and Vmax for BENZO amine production by whole liver homogenates were 0.148 mM and 1.45 nmole min-1 mg-1 protein respectively. Tumour homogenates were less active than liver; e.g. Vmax for the KHT tumour was 6-10-fold lower.
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PMID:Nitroimidazole bioreductive metabolism. Quantitation and characterisation of mouse tissue benznidazole nitroreductases in vivo and in vitro. 310 39

Cytochrome P-450LA omega purified from clofibrate-induced rat liver oxidizes lauric acid to 11- and 12-hydroxydodecanoic acid in approximately a 1:17 ratio at a rate of 20 nmol/nmol P-450/min. In contrast, cytochrome P-450b oxidizes lauric acid much more slowly (0.5 nmol/nmol P-450/min) to an 8:1 mixture of the same metabolites. Western blot analysis indicates that P-450LA omega accounts for 1-2 and 16-30%, respectively, of the total cytochrome P-450 in uninduced and clofibrate-induced rat liver. Cytochrome b5 increases the efficiency of omega-hydroxylation but not the rate of catalytic turnover. Incubation of the enzyme with 10-undecynoic acid (10-UDYA) results in loss of approximately 45% of the enzymatic activity but none of the enzyme chromophore. Approximately 1 mol of 1,11-undecandioic acid is produced per mole of inactivated enzyme. This extraordinary inactivation efficiency is confirmed by NADPH consumption studies. Approximately 0.5 equivalents of label are covalently bound to the enzyme when it is incubated with 14C-labeled 10-UDYA. 11-Dodecenoic acid appears not to be a substrate for cytochrome P-450LA omega but is oxidized, presumably by a contaminating isozyme, to a 10:1 mixture of 11,12-epoxydodecanoic acid and 12-oxododecanoic acid. The results suggest the presence of two closely related P-450LA omega enzymes, only one of which is susceptible to inactivation by 10-UDYA. They also indicate that cytochrome P-450LA omega has a highly structured active site that sterically suppresses omega-1-hydroxylation in order to deliver the oxygen to the thermodynamically disfavored terminal carbon. Protein rather than heme alkylation follows from this reaction regiospecificity.
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PMID:The catalytic site of rat hepatic lauric acid omega-hydroxylase. Protein versus prosthetic heme alkylation in the omega-hydroxylation of acetylenic fatty acids. 319 93

Highly purified cytochrome P-450 11 beta-/18-hydroxylase and the electron carriers adrenodoxin and adrenodoxin reductase were prepared from porcine adrenal. When the enzyme was incubated with the electron carriers, 11-deoxycorticosterone (DOC) and NADPH, the following products were isolated and measured by HPLC: corticosterone, 18-hydroxy-11-deoxycorticosterone (18-hydroxyDOC), 18-hydroxycorticosterone and aldosterone. All of the DOC consumed by the enzyme can be accounted for by the formation of these four steroids. Aldosterone was identified by mass spectroscopy and by preparing [3H]aldosterone from [3H]corticosterone followed by recrystallization at constant specific activity after addition of authentic aldosterone. Corticosterone and 18-hydroxycorticosterone were also converted to aldosterone. Conversion of corticosterone and 18-hydroxycorticosterone to aldosterone required P-450, both electron carriers, NADPH and substrate. The reaction is inhibited by CO and metyrapone. Moreover, all three activities of the purified enzyme decline at the same rate when the enzyme is kept at room temperature for various periods of time and when the enzyme is treated with increasing concentrations of anti-11 beta-hydroxylase (IgG) before assay. It is concluded that cytochrome P-450 11 beta-/18-hydroxylase can convert DOC to aldosterone via corticosterone and 18-hydroxycorticosterone. The stoichiometry of this conversion was found to be 3 moles of NADPH, 3 moles of H+ and 3 moles of oxygen per mole of aldosterone produced.
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PMID:Conversion of 11-deoxycorticosterone and corticosterone to aldosterone by cytochrome P-450 11 beta-/18-hydroxylase from porcine adrenal. 338 33


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