Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: KEGG:D02011 (FAD)
 5,530 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rat liver microsomes exhibit nifurtimox (NFX) nitroreductase activity, which is mostly NADPH-dependent and is completely abolished by heating and under an atmosphere of air. Pure carbon monoxide inhibits for 28% microsomal NFX nitroreductase activity while FAD 1 mM significantly enhances it. Smaller activities than in liver were found in brain, small intestine, testes, lung and heart. Rat liver cytosol also showed NFX nitroreductase activity using either hypoxanthine or N-methylnicotinamide as substrates. These activities were inhibited by allopurinol or menadione respectively. Results suggest that cytochrome P-450, NADPH cytochrome c reductase, xanthinoxidase and aldehyde oxidase are able to reduce NFX nitrogroups in rat liver and other tissues.
 ...
PMID:Studies on nifurtimox nitroreductase activity in liver and other rat tissues. 649 2

Antibodies to NADPH-cytochrome P-450 reductase have been used to essentially abolish the contribution of cytochrome P-450 to xenobiotic metabolism by mammalian microsomes. This permits the determination of the activity of the FAD-containing mono-oxygenase and the stoichiometry between substrate, O2 and NADPH, in the microsomal membrane, and in the absence of cytochrome P-450-dependent activity. FAD-containing mono-oxygenase oxidation rates were determined for sulphur- and nitrogen-containing substrates, including: thiols; sulphides; thioamides; primary, secondary and tertiary amines; hydrazines. Although the enzyme in mouse, rabbit, rat and pig microsomes displays similar substrate specificity, some catalytic characteristics are different between species and tissues.
 ...
PMID:The measurement of FAD-containing mono-oxygenase activity in microsomes containing cytochrome P-450. 650 63

The enzymic N-oxidation of a series of N-unsubstituted basic benzamidines (I) to a new type of metabolite, the amidoximes (II), is reported. Rabbit liver homogenates (9000 g supernatant) were used as enzyme source, and metabolites were identified by t.l.c. and mass spectral analysis using synthetic reference compounds. The microsomal NADPH- and oxygen-dependent hydroxylation of benzamidines was not detected after incubation of benzamidine in the presence of SKF 525-A, a known inhibitor of cytochrome P-450. Neither benzamidine or p-methoxybenzamidine is a good substrate for purified microsomal FAD-containing mono-oxygenase.
 ...
PMID:The N-oxidation of benzamidines in vitro. 664 80

Benznidazole (Bz) (N-benzyl-2-nitro-1-imidazole-acetamide) is a drug used against Chagas' disease. Rat liver microsomal and cytosolic fractions, but not mitochondria, exhibited Bz nitroreductase activity under anaerobic conditions in the presence of NADPH. Microsomal nitroreductase activity was enhanced by FAD and was inhibited totally by oxygen and partially by carbon monoxide. Liver cystosol fraction was able to reduce Bz nitrogroups in the presence of either N-methylnicotinamide or hypoxanthine as substrates. These enzyme activities were inhibited by menadione or allopurinol respectively. Under every experimental condition leading to enzymatic reduction of Bz nitrogroups and its inhibition or enhancement, reactive metabolites that bind covalently to proteins were also produced. This covalent binding was effectively prevented by reduced glutathione. Results suggest the participation of cytochrome P-450 and cytochrome c reductase in liver microsomal processes and of xanthine oxidase and aldehyde oxidase in liver cytosolic processes of Bz nitroreduction and activation to reactive metabolites that bind covalently to proteins. Possible pharmacological and toxicological implications of the described observations were discussed.
 ...
PMID:Reductive metabolism and activation of benznidazole. 671 14

To evaluate the different contributions of either microsomal FAD-containing ( FADM ) or cytochrome P-450 dependent monooxygenases in the bioactivation and liver toxicity of thioacetamide-S-oxide ( TASO ) (a proximate metabolite of the liver toxin and carcinogen thioacetamide), this compound: (i) was given to rats pretreated with methimazole (a substrate and inhibitor of FADM ), SKF 525-A (an inhibitor of cytochrome P-450) and cobalt protoporphyrin IX (a synthetic porphyrin which induces a long-lasting depletion of the hepatic cytochrome P-450); and (ii) was added to liver microsomes performing oxidation of model FADM or cytochrome P-450 substrates. Whereas the prior administration of methimazole alleviated the TASO induced liver necrosis, SKF 525-A was almost ineffective. Also pretreatment with cobalt protoporphyrin IX prevented liver necrosis. However, this porphyrin derivative was found to depress both cytochrome P-450 dependent and the FADM dependent biotransformations. On the other hand, addition of TASO to liver microsomes in vitro induced changes in the kinetics of S-oxidation of thiobenzamide and of N-oxidation of dimethylaniline, whereas the O-deethylation of ethoxycoumarin was unchanged. The overall results show the necessity of TASO bioactivation by mixed-function monooxygenases for the toxic action to be apparent; at the same time, the findings suggest FADM as the system mainly involved in TASO metabolism.
 ...
PMID:Role of the microsomal FAD-containing monooxygenase in the liver toxicity of thioacetamide S-oxide. 672 35

Rat liver microsomal NADPH-cytochrome P-450 reductase was prepared free of detectable amounts of FMN by a new procedure based on the exchange of this flavin into apoflavodoxin. The resulting FMN-free reductase binds NADP in the oxidized state with the same affinity (Kd = 5 microM) and stoichiometry (1:1 molar ratio) as does the native enzyme. Both the native and FMN-free reductase catalyze rapid reduction of ferricyanide, but the ability to reduce th 5,6-benzoflavone-inducible form of the liver microsomal cytochrome P-450 (P-450LM4) is lost upon removal of FMN. The FMN-free enzyme was reconstituted with artificial flavins which, in the free state, have oxidation-reduction potentials ranging from -152 to -290 mV, including 5-carba-5-deaza-FMN and several FMN analogs with a halogen or sulfur substituent on the dimethylbenzene portion of the ring system. Enzyme reconstituted with 5-carba-5-deaza-FMN has catalytic properties which are not significantly different from those of the FMN-free reductase, and is unable to reduce P-450LM4. On the other hand, the ability to reduce P-450LM4 and the other FMN-dependent activities of the native reductase are restored by substitution of several other analogs for FMN, but the kinetics of P-450LM4 reduction, studied under anaerobic conditions by stopped flow spectrophotometry, are significantly altered. The oxidation-reduction behavior of enzyme reconstituted with 7-nor-7-Br-FMN is substantially different from that of the native enzyme, and less thermodynamic stabilization of the semiquinone is observed with this flavin analog. In contrast, the oxidation-reduction properties of enzyme containing 8-nor-8-mercapto-FMN are similar to those of the native enzyme, but the spectral properties are significantly different. As shown in a stopped flow experiment, reduction of this FMN analog precedes reduction of P-450LM4 when a complex of the flavoprotein and P-450LM4 is allowed to react with NADPH. Our experiments support a sequence of electron transfer in this enzyme system as follows: NADPH leads to FAD leads to FMN leads to P-450. We propose that the enzyme cycles between a le- and a 3e-reduced state during turnover and that electrons are donated to acceptors via the reaction, FMNH2 leads to FMNH ..
 ...
PMID:Separate roles for FMN and FAD in catalysis by liver microsomal NADPH-cytochrome P-450 reductase. 677 61

The mechanism of hepatic NADPH-cytochrome P-450 reductase has been investigated by using a stopped-flow technique. The reduction of the oxidized native enzyme (FAD-FMN) by NADPH proceeds by both one-electron equivalent and two-electron eqiuvalent mechanisms. The air-stable semiquinone form (FAD-FMNH.) of the native enzyme, which is characterized by an absorption shoulder at 635 nm, is also rapidly reduced to another semiquinone form (FADH-FMNH2) by NADPH with the disappearance of the shoulder at 635 nm, but the absorbance change at 585 nm is relatively constant. The FAD moiety in the FMN-depleted enzyme is rapidly reduced by NADPH, and reduced FAD is oxidized in successive one-electron steps by O2 or potassium ferricyanide. These results indicate the possibility of intra-molecular one-electron transfer between FAD and FMN. The rate of cytochrome P-450 reduction decreases in the presence of FMN-depleted enzyme but is nearly restored to the value of the original enzyme with FMN-reconstituted enzyme. These data suggest that FAD is the low-potential flavin, which serves as an electron acceptor from NADPH. On the other hand, FMN, which is the high-potential flavin, appears to participate as an electron carrier in the process of electron transfer from NADPH to cytochrome P-450 during the mixed-function catalytic cycle.
 ...
PMID:Studies on the microsomal mixed-function oxidase system: mechanism of action of hepatic NADPH-cytochrome P-450 reductase. 678 58

Squalene epoxidase (EC 1.14.99.7, squalene 2,3-monooxygenase (epoxidizing) was purified to an apparent homogeneity from rat liver microsomes. The purification was carried out by solubilization of microsomes by Triton X-100, fractionation with ion exchangers, hydroxyapatite, Cibacron Blue Sepharose 4B, and chromatofocusing column chromatography. A total purification of 143-fold over the first DEAE-cellulose fraction was achieved. The purified enzyme gave a single major band on SDS-polyacrylamide gel electrophoresis and the Mr was estimated to be 51 000 as a single polypeptide chain. The enzyme showed no distinct absorption spectrum in the visible regions. The squalene epoxidase activity was reconstituted with the purified enzyme, NADPH-cytochrome P-450 reductase (EC 1.6.2.4), FAD, NADPH and molecular oxygen in the presence of Triton X-100. The apparent Michaelis constants for squalene and FAD were 13 microM and 5 microM, respectively. The Vmax was about 186 nmol per mg protein per 30 min for 2,3-oxidosqualene. The enzyme activity was not inhibited by potent inhibitors of cytochrome P-450. It is suggested that squalene epoxidase is distinct from cytochrome P-450 isozymes.
 ...
PMID:Purification and partial characterization of squalene epoxidase from rat liver microsomes. 681 96

In the presence of NADPH and under aerobic conditions, thioether-containing organo-phosphorus and carbamate pesticides were oxidized by the FAD-dependent monooxygenase (EC 1.14.13.8) purified from pig liver microsomes. The stoichiometric relationship between NADPH and substrate during the course of the reaction was 1:1, and the product, in the case of disulfoton and phorate, was the sulfoxide. The product was optically active and further oxidation to the sulfone was not apparent. Furthermore, the sulfoxides of disulfoton, phorate and croneton were not substrates for this enzyme. n-Octylamine, a known cytochrome P-450 inhibitor, increased the rate of sulfoxidation reactions catalyzed by the FAD-dependent monooxygenase. Structure-activity relationships were investigated using thirty-nine possible substrates. Structural changes around the thioether sulfur that affect nucleophilicity or that cause steric hindrance tended to decrease the sulfoxidation rats. With phosphorodithioates, changes around the phosphorus atom also affected oxidation of the thioether sulfur. Although neither the thiono nor the thiol sulfur atoms were attacked, substitution of either sulfur by oxygen decreased sulfoxidation. Thioether-containing O, O-dimethyl phosphorodithioates were not oxidized as readily as their O, O-diethyl analogs. Tetram and its analogs, which contain a teritiary amine group, were also substrates for this enzyme, presumably forming the N-oxide.
 ...
PMID:Sulfoxidation of thioether-containing pesticides by the flavin-adenine dinucleotide- dependent monooxygenase of pig liver microsomes. 708 42

1. A continuous spectrophotometric determination of rat hepatic microsomal anaerobic azo reductase activity has been developed. 2. The addition of soluble flavins (riboflavin, FMN or FAD) greatly increased this NADPH-dependent activity towards a number of azo substrates. 3. Investigations with amaranth as substrate gave an apparent Km of 34 microM and Vmax. of 4 nmol/min per mg of microsomal protein. The inclusion of a fixed concentration of FMN increased Vmax. and greatly decreased Km, the magnitude of these changes reflecting the concentration of flavin present. 4. Investigations using a fixed amaranth concentration over a range of flavin concentrations gave biphasic double-reciprocal plots with two apparent Km and Vmax. values. 5. Pretreatment of animals with cobaltous chloride, 2-allyl-2-isopropylacetamide, carbon tetrachloride, phenobarbitone and 3-methylcholanthrene altered azo reductase activity in parallel with changes in cytochrome P-450 content. 6. The significance of these results is discussed in terms of the electron-transfer components present in the hepatic microsomal fraction.
 ...
PMID:A continuous spectrophotometric determination of hepatic microsomal azo reductase activity and its dependence on cytochrome P-450. 709 14


<< Previous 1 2 3 4 5 6 7 Next >>