Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Formation of catecholestrogens (CE) by rat hepatic microsomes was re-examined because as recently shown; (1) CE formation can be catalyzed by an NADPH-dependent estrogen-4-hydroxylase (E-4-H(NADPH)) and by a peroxidatic, organic hydroperoxide-dependent estrogen-2/4-hydroxylase (E-2/4-H(OHP)), in addition to the established NADPH-dependent estrogen 2-hydroxylase (E-2-H(NADPH)); and (2) the indirect radiometric and the COMT-coupled radioenzymatic assays, used in many previous studies, may fail to provide an accurate measure, in particular, of 4-OH-CE. Using a direct product isolation assay, hepatic microsomes of both male and female rats were shown to express E-2/4-H(OHP) activity with properties similar to those of peroxidatic activity in other tissues. The activities of E-2/4-H(OHP) and E-2-H(NADPH) were affected differently by 5 out of 7 inducers of cytochromes P-450 administered in vivo. Phenobarbital and dexamethasone caused a 4- and 2-3-fold increase in E-2-H(NADPH) activity, respectively, but only a 38 and 20% increase in E-2/4-H(OHP) activity. Ketoconazol and beta-naphtoflavone caused a modest increase in E-2-H(NADPH) activity but a decrease in OHP-dependent activity. Clofibrate decreased peroxidatic activity by 50% and NADPH-dependent activity by approximately 20%. Both activities were increased by ethanol but decreased by isoniazide, an agent which induces the same form of cytochromes P-450 as ethanol. Polyclonal antibody against P-450p, a form of P-450 induced by glucocorticoids, inhibited E-2-H(NADPH) but not E-2/4-H(OHP) activity of untreated and of dexamethasone- and phenobarbital-treated rats. This study establishes that CE formation may occur in liver via the peroxidatic pathway and indicates that this pathway depends on forms of P-450 different from those mediating E-2-H(NADPH) activity. It also confirms and extends previous observations of the involvement of multiple, constitutive and induced forms of cytochrome P-450 in NADPH-dependent 2-hydroxylation in liver.
J Steroid Biochem Mol Biol 1990 Oct
PMID:Hepatic catecholestrogen synthases: differential effect of sex, inducers of cytochromes P-450 and of antibody to the glucocorticoid inducible cytochrome P-450 on NADPH-dependent estrogen-2-hydroxylase and on organic hydroperoxide-dependent estrogen-2/4-hydroxylase activity of rat hepatic microsomes. 217 38

Studies with biomimetic models can yield considerable insight into mechanisms of enzymatic catalysis. The discussion above indicates how such information has been important in the cases of flavoproteins, hemoproteins, and, to a lesser extent, the copper protein dopamine beta-hydroxylase. Some of the moieties that we generally accept as intermediates (i.e., high-valent iron oxygen complex in cytochrome P-450 reactions) would be extremely hard to characterize were it not for biomimetic models and more stable analogs such as peroxidase Compound I complexes. Although biomimetic models can be useful, we do need to keep them in perspective. It is possible to alter ligands and aspects of the environment in a way that may not reflect the active site of the protein. Eventually, the model work needs to be carried back to the proteins. We have seen that diagnostic substrates can be of considerable use in understanding enzymes and examples of elucidation of mechanisms through the use of rearrangements, mechanism-based inactivation, isotope labeling, kinetic isotope effects, and free energy relationships have been given. The point should be made that a myriad of approaches need to be applied to the study of each enzyme, for there is potential for misleading information if total reliance is placed on a single approach. The point also needs to be made that in the future we need information concerning the structures of the active sites of enzymes in order to fully understand them. Of the enzymes considered here, only a bacterial form of cytochrome P-450 (P-450cam) has been crystallized. The challenge to determine the three-dimensional structures of these enzymes, particularly the intrinsic membrane proteins, is formidable, yet our further understanding of the mechanisms of enzyme catalysis will remain elusive as long as we have to speak of putative specific residues, domains, and distances in anecdotal terms. The point should be made that there is actually some commonality among many of the catalytic mechanisms of oxidation, even among proteins with different structures and prosthetic groups. Thus, we see that cytochrome P-450 has some elements of a peroxidase and vice versa; indeed, the chemistry at the prosthetic group is probably very similar and the overall chemistry seems to be induced by the protein structure. The copper protein dopamine beta-hydroxylase appears to proceed with chemistry similar to that of the hemoprotein cytochrome P-450 and, although not so thoroughly studied, the non-heme iron protein P. oleovarans omega-hydroxylase.(ABSTRACT TRUNCATED AT 400 WORDS)
Crit Rev Biochem Mol Biol 1990
PMID:Enzymatic oxidation of xenobiotic chemicals. 218 70

Cytochrome P-450-dependent enzyme activities have been determined in malarial parasites. Both Plasmodium berghei and Plasmodium falciparum parasites exhibited activity and these activities were greater in chloroquine resistant parasites than in sensitive strains. This enzyme activity could be induced by phenobarbitone and inhibited by specific inhibitors of the cytochrome P-450 family of enzymes. The significance of these observations in parasite drug resistance is discussed.
Mol Biochem Parasitol 1990 Jun
PMID:Cytochrome P-450 activity in malarial parasites and its possible relationship to chloroquine resistance. 220 31

The reaction of NalO4, highly purified flavin-containing monooxygenase (EC 1.14.13.8), and microsomes from hog liver with 2-aryl-1,3-dithiolanes and 2-aryl-1,3-dithiolane S-oxides was investigated. The initial rates determined for the microsome- and purified flavin-containing monooxygenase-catalyzed rate of S-oxidation of para-substituted 2-aryl-1,3-dithiolanes were similar, demonstrating that S-oxidation of these substrates occurred with similar velocities at saturating concentrations of substrate and, at least for the first S-oxidation, the reaction was insensitive to the nature of the para-substituent. The diastereoselectivity of S-oxygenation of 2-aryl-1,3-dithiolanes was determined and, in general, a marked preference for addition of oxygen to the sulfide sulfur atom was observed to occur trans to the aryl groups. In all cases examined, enantioselective enzymatic S-oxidation was observed. For S-oxide formation in microsomes, the data provided evidence for a minor role of cytochrome P-450 in S-oxide formation, but the flavin-containing monooxygenase was mainly responsible for production of S-oxide. In contrast to previous reports, the enantioselectivity of S-oxidation catalyzed by highly purified cytochrome P-450IIB-1 and cytochrome P-450IIB-10 was not always opposite to that catalyzed by hog liver flavin-containing monooxygenase activity. 2-Aryl-1,3-dithiolane S-oxides were also oxidized a second time by NalO4, microsomes, or highly purified flavin-containing monooxygenase from hog liver but not cytochrome P-450IIB-1 or P-450IIB-10. The rate of the second oxidation was 10-15-fold slower than the corresponding first S-oxidation and S,S'-dioxide formation was markedly dependent on the electronic nature of the para-substituent (Hammett correlation rho value of -1.3 and -1.1 for microsomes and highly purified flavin-containing monooxygenase from hog liver, respectively). The large dependence of the rate of S,S'-dioxide formation on the nature of the para-substituent demonstrates that velocity values at saturating concentrations of S-oxide were not the same for all 2-aryl-1,3-dithiolane S-oxides and suggests that the chemical nature of the 2-aryl-1,3-dithiolane S-oxide contributes to the rate-determining step of this enzymatic reaction.
Mol Pharmacol 1990 Oct
PMID:Stereoselective S-oxygenation of 2-aryl-1,3-dithiolanes by the flavin-containing and cytochrome P-450 monooxygenases. 223 94

Hepatic ischemia induced in vivo by ligation of the left hepatic lobe of rats for up to 2 hr had no effect on cytochrome P-450, cytochrome c reductase, or lobe histology; however, cytochrome b5 increased with ischemia duration. Ethylmorphine demethylation decreased 35% after 2 hr of ischemia. Reperfusion of tissue previously made ischemic for up to 2 hr was associated with appreciable necrosis as well as decreases in cytochrome P-450, cytochrome b5, cytochrome c reductase, and ethylmorphine demethylation. Serum alanine transaminase and aspartate transaminase concentrations were increased by reperfusion of previously ischemic tissue. Reperfusion of the previously ischemic lobe for 18 hr was associated with a greater loss of cytochromes P-450 and b5, cytochrome c reductase, and ethylmorphine demethylation than reperfusion for 1 hr. The total decrease in cytochrome P-450 and b5 content was equal to the decrease in total microsomal heme content, although cytochrome P-450 decreased more than cytochrome b5. Ethoxyresorufin deethylation by hepatic microsomes from 3-methylcholanthrene-treated rats was decreased by ischemia-reperfusion; however, pentoxyresorufin dealkylation by hepatic microsomes from phenobarbital-treated rats was not, suggesting specific cytochrome P-450 isozyme loss. In vitro NADPH-dependent lipid peroxidation in hepatic microsomes from control and phenobarbital- and 3-methylcholanthrene-treated rats resulted in a selective decrease of ethoxyresorufin but not pentoxyresorufin dealkylation, similar to that observed in livers subjected to ischemia-reperfusion in vivo. These data suggest that cytochrome P-450, ethylmorphine demethylation, and ethoxyresorufin deethylation are more susceptible to ischemia-reperfusion injury than cytochrome b5 or pentoxyresorufin dealkylation.
Mol Pharmacol 1990 Dec
PMID:Effects of hepatic ischemia-reperfusion injury on the hepatic mixed function oxidase system in rats. 225 Jun 63

Several synthetic flavones were found to inhibit the aromatization of androstenedione to estrone catalyzed by human placental microsomes. Twenty-one compounds were tested and the IC50 of the most active were: flavone, 10 microM; 7-hydroxyflavone, 0.5 microM; 7,4'-dihydroxyflavone, 2.0 microM; flavanone, 8.0 microM; and 4'-hydroxyflavanone, 10 microM. Most of the others had IC50 values ranging from 80 to greater than 200 microM. These findings show that 4'-hydroxylation results in either no change or very little change in IC50 for flavanone, isoflavone and isoflavanone as well as other ring A hydroxylated flavones. Derivatives of flavone with a hydroxyl substituent at position 5, 6 and 7 were also screened. 7-Hydroxyflavone (11) was the most effective competitive inhibitor (IC50 = 0.5 microM) with an apparent Ki value of 0.25 microM. Compound 11 also induced a change in the absorption spectrum of the aromatase cytochrome P-450 which is indicative of substrate displacement. The relative binding affinities of the flavonoid analogs were determined and only ring A adn ring B dihydroxylated analogs were found to bind to the estrogen receptor.
J Steroid Biochem Mol Biol 1990 Oct
PMID:Aromatase inhibition by flavonoids. 226 57

Activities of aromatase cytochrome P-450 in the columnar epithelial region (CE), squamous epithelial region (SE) and connective tissue (CT) of uterine cervix, and endometrium (EM) during the menstrual cycle were determined using [4-14C] and [1 beta-3H]androstenedione. Aromatase activities in the proliferative phase (n = 8) were 15.0 +/- 7.9, 10.9 +/- 10.3, 9.4 +/- 10.6 and 8.0 +/- 7.3 (mean +/- SD) fmol/h/mg protein in CE, SE, CT and EM, respectively, and aromatase activities in the secretory phase (n = 6) were 31.5 +/- 7.6, 19.1 +/- 7.1, 5.6 +/- 4.6 and 6.3 +/- 1.5 fmol/h/mg protein, respectively. The results show that the aromatase activities in these regions in the proliferative phase were not significantly different from each other. On the other hand, the aromatase activity in the secretory phase was significantly higher in CE than in any other regions (P less than 0.05), and significantly higher in SE than in CT or EM (P less than 0.05). There was no significant difference in aromatase activity between CT and EM. By comparison of aromatase activity between these two phases, the activity in CE was significantly higher in the secretory phase than in the proliferative phase (P less than 0.05), but no significant difference was observed in other regions.
J Steroid Biochem Mol Biol 1990 Dec 10
PMID:Distribution and cyclic change of aromatase cytochrome P-450 activity in human uteri. 227 58

The arene oxides formation energy for about 30 benzene derivatives were calculated in frames of MO LCAO method. The benzene derivatives are typical substrates of cytochrome P-450 catalyzed aromatic oxidation. The relationship between the formation energy of tetrahedral type arene oxides and the relative reactivity of substrates toward microsomal hydroxylation was found. The formation energy of arene oxides correlates also with toxicity of benzene derivatives. Some limitations of the oxenoid model are discussed.
Mol Biol (Mosk)
PMID:[The oxenoid model of the mechanism of activating molecular oxygen by cytochrome p450: the role of substrate structure]. 229 Apr 28

Cortisol production from cholesterol requires the activity of four steroid hydroxylases: cholesterol side chain cleavage cytochrome P-450 (P-450scc), 17 alpha-hydroxylase cytochrome P-450 (P-45017 alpha), 21-hydroxylase cytochrome P-450 (P-450C21) and 11 beta-hydroxylase cytochrome P-450 (P-45011 beta). We have previously shown that transformed, nonsteroidogenic COS 1 cells derived from monkey kidney are a useful system for expression of various forms of cytochrome P-450. The present study shows that COS 1 cell cultures multiply transfected with six plasmids containing all four steroid hydroxylases, 3 beta-hydroxysteroid dehydrogenase/delta 5----4-isomerase (3 beta HSD) and adrenodoxin produce cortisol and aldosterone when 22(R)-hydroxycholesterol is supplied to the system. When pregnenolone is used as substrate, various intermediate metabolites are detected at different time points further establishing the incorporation of complete functional steroidogenic pathways into the nonsteroidogenic cell cultures. Since the first and the last reactions in these pathways take place in the mitochondrion, the movement of various intermediate metabolites from mitochondrion to endoplasmic reticulum and back to mitochondrion occurs in and between COS 1 cells.
Mol Cell Endocrinol 1990 Oct 01
PMID:Incorporation of steroidogenic pathways which produce cortisol and aldosterone from cholesterol into nonsteroidogenic cells. 229 41

Liver, kidney, and lung microsomes prepared from nonpretreated female Sprague-Dawley rats catalyze the NADPH- and oxygen-dependent S-oxygenation of para-methoxyphenyl-1,3-dithiolane. Studies on the biochemical mechanism of dithiolane S-oxygenation in liver, kidney, and lung microsomes suggest that this reaction is catalyzed in a diastereoselective and enantioselective fashion by the flavin-containing monooxygenase and, to a lesser extent, the cytochromes P-450. This conclusion is based on results examining the effects of selective cytochrome P-450 inhibitors and positive effectors, microsome heat-inactivation treatment, and alternate substrates for the flavin-containing monooxygenase. Liver and kidney microsomes prepared from ovarectomized female rats tended to have decreased S-oxygenase activity, compared with nonpretreated female rats, whereas ovarectomized rats pretreated with estradiol had markedly lower S-oxygenase activity. In contrast, lung microsomal S-oxygenase activity, which is low in pulmonary microsomes from nonpretreated female rats, increases 2-4-fold after ovariectomization and estradiol pretreatment. In female Sprague-Dawley rats, estradiol pretreatment is mainly responsible for the large decrease (or increase) in S-oxygenase activity observed in the tissues examined, although it is unlikely that estradiol alone controls flavin-containing monooxygenase S-oxygenase activity.
Mol Pharmacol 1990 Feb
PMID:Enantioselective S-oxygenation of para-methoxyphenyl-1,3-dithiolane by various tissue preparations: effect of estradiol. 230 55


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