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1.
A.J. Marinello H.L. Gurtoo R.F. Struck B. Paul 《Biochemical and biophysical research communications》1978,83(4):1347-1353
Cyclophosphamide (CP) metabolites, acrolein and 4-hydroxy-CP, were found to denature rat liver microsomal cytochrome P-450, whereas another metabolite, phosphoramide mustard, CP or its analog Ifosfamide had no effect. The denaturation produced by CP metabolites could be blocked by cysteine, suggesting an interaction between CP metabolite(s) and sulfhydryl groups in cysteine and probably in cytochrome P-450. These studies might explain the biochemical basis of the specific depression of various microsomal mixed function oxygenase activities produced by high doses of CP. 相似文献
2.
M.J. Berrigan H.L. Gurtoo S.D. Sharma R.F. Struck A.J. Marinello 《Biochemical and biophysical research communications》1980,93(3):797-803
Cyclophosphamide (CP) at high or repeated doses results in the depression of mixed function oxygenase activities of the liver. Recent studies have attributed this to the interaction between acrolein, a metabolite of CP, and sulfhydryl groups in cytochrome P-450. The present report demonstrates the protection afforded by N-acetylcysteine against acrolein-induced denaturation of cytochrome P-450 and CP-related depression of mixed function oxygenase . Co-administration of CP and innocuous chemicals that provide free sulfhydryl groups should, in the future, be useful in enhancing the therapeutic index of CP by either reducing some of the toxicity and/or by allowing the use of repeated treatment with lower but effective doses of CP. 相似文献
3.
The effect of pretreatment with phenobarbitone, rifampicin, β-naphthoflavone, antipyrine and spironolactone on the irreversible binding of ethynyloestradiol to guinea pig liver microsomes has been examined and the corresponding changes in microsomal P-450 content and cytochrome reductase activity measured. Rifampicin produced the greatest increase (220%) in irreversible binding while phenobarbitone produced the greatest increase in both microsomal P-450 content (172%) and cytochrome reductase activity (210%). There was no correlation of irreversible binding with either microsomal P-450 content or with cytochrome reductase activity. 相似文献
4.
Peter R. Alefounder Stuart J. Ferguson 《Biochemical and biophysical research communications》1982,104(3):1149-1155
The nitrous oxide reductase activity of can be conveniently measured using an electrochemical method for determining N2O. Introduction of this procedure has shown that (i) N2O reductase activity is reversibly inhibited by oxygen; (ii) antimycin strongly inhibits electron flow to N2O and that the inhibition is bypassed by tetramethyl-p-phenylenediamine; (iii) ascorbate plus tetramethyl-p-phenylenediamine, presumably by donating electrons to cytochrome c, is an effective reductant for nitrous oxide reductase; (iv) in the presence of the nitrous oxide reductase inhibitor, acetylene, N2O is promptly produced from nitrite, consistent with the product of nitrite reductase being N2O. 相似文献
5.
Rat liver microsomal NADH-cytochrome reductase activity is stimulated by 20 μM thyroxine . Thyroxine does not influence microsomal NADH-dichlorophenolindophenol reductase, NADPH-cytochrome reductase, or NADPH-dichlorophenolindophenol reductase activity. Stimulation of NADH-cytochrome reductase activity is not mediated by super-oxide and is likely due to enhanced reduction or oxidation of cytochrome 5. 相似文献
6.
Antimycin, when added to resolved succinate-cytochrome reductase complex in amounts sufficient to partially inhibit succinate-cytochrome reductase activity, causes a decrease in inhibition of the residual succinate-cytochrome reductase activity by 2-thenoyltrifluoroacetone. Antimycin has no effect on the inhibition of succinate-ubiquinone reductase activity by 2-thenoyltrifluoroacetone. We propose that antimycin increases the steady state concentration of ubisemiquinone in the reductase complex, and that 2-thenoyltrifluoracetone is competitive with ubisemiquinone. 相似文献
7.
M Yamaguchi T Yamauchi H Fujisawa 《Biochemical and biophysical research communications》1975,67(1):264-271
Benzoate 1,2-dioxygenase system which catalyzed double hydroxylation of benzoate was obtained from and was shown to consist of two protein components (component A and B). Component A which was purified and was shown to be homogeneous upon sodium dodecyl sulfate disc gel electrophoresis retained high activity of NADH-cytochrome reductase. Both of benzoate 1,2-dioxygenase activity and NADH-cytochrome reductase activity were simultaneously induced by benzoate. Dichlorophenolindophenol which could serve as an electron acceptor of the NADH-cytochrome reductase inhibited the activity of benzoate 1,2-dioxygenase. These results suggest the possibility that NADH-cytochrome reductase activity is required for benzoate 1,2-dioxygenase. 相似文献
8.
Isolated heterocysts of the N2-fixing blue-green alga Anabaena cylindrica contain the Photosystem I components P-700, bound and soluble ferredoxins and ferredoxin-NADP reductase. They also show Photosystem I activity being able to photoreduce both methylviologen and NADP when ascorbate+dichlorophenol-indophenol acts as reductant. They photophosphorylate (64 μmol ATP produced/mg chlorophyll ) and carry out oxidative phosphorylation (8.7 μmol ATP produced/mg chlorophyll ). Ninety per cent of the total cell-free extract nitrogenase activity is located in the heterocyst fraction of aerobic cultures. 相似文献
9.
J LeGall W J Payne T V Morgan D DerVartanian 《Biochemical and biophysical research communications》1979,87(2):355-362
Nitrite reductase (cytochrome ) from has been crystallized in high yield in three simple and rapid steps. The spectral absorption ratio at 408 to 280 nm was 1.52. Light absorption spectra in the oxidized and reduced states were virtually identical to those of nitrite reductase from . EPR spectroscopy of nitrite reductase at 12° showed a low-spin ferric heme resonance with g-values at 2.52, 2.45 and 1.73 assigned to the d-heme. Reaction of nitrite reductase with nitrite in the presence of the reducing systems [(ascorbate + PMS) or sulfide] resulted in the formation of nitric oxide (confirmed by gas chromatography) which reacted with both - and -hemes of nitrite reductase yielding an EPR-detectable enzyme-NO complex with g-values at 2.07, 2.04 and 1.99 and a 14N hyperfine splitting constant of 22.5 gauss. The amount of nitric oxide produced enzymatically with sulfide as electron donor was only 5% of that found when ascorbate plus PMS served as reductant.To our knowledge the detection of the unique enzyme-NO complex is the first definitive EPR evidence for the mandatory liganding of nitric oxide with pure nitrite reductase during nitrite reduction. 相似文献
10.
The role of molybdenum in formation of the NADPH-nitrate reductase by Aspergillus nidulans 总被引:1,自引:0,他引:1
R J Downey 《Biochemical and biophysical research communications》1973,50(3):920-925
Non-nitrate reducing mutants of have been noted to produce either a nitrate inducible or constitutive NADPH-cytochrome reductase which resides in either a 4.5s or a 7.8s protein. The latter closely resembles the nitrate inducible, FAD dependent NADPH-nitrate reductase from the wild type. Measurement of flavin adenine dinucleotide (FAD) and molybdenum (Mo) in these two proteins revealed significant differences particularly in Mo. The concepts that a nitrate inducible gene product constitutes the major flavin bearing component of the enzyme and that a constitutively produced gene product is implicated in formation of the larger Mo bearing multimer are further supported. 相似文献
11.
B L Currie J Warberg K Folkers 《Biochemical and biophysical research communications》1977,79(4):1207-1211
The hypocholesterolemic drug clofibrate (ethyl-α--chlorophenoxyisobutyrate) was found to strongly suppress 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34) activity in cultured mouse L cells at concentrations of 20 – 50 μg/ml. The half-life () of the reductase (approximately 120 min) was strongly reduced when L cells were incubated with cycloheximide plus a maximal inhibitory concentration of clofibrate (50 μg/ml), resulting in a value of 10 min. Preliminary kinetic analysis of the inhibition suggested that clofibrate increased the rate of inactivation (or degradation) of the reductase without affecting the rate of enzyme synthesis. 相似文献
12.
Wolfgang Feller Hartmut Follmann 《Biochemical and biophysical research communications》1976,70(3):752-758
A ribonucleoside diphosphate reductase is demonstrated in the algae, and . In synchronized cultures an activity maximum at the 12th hour of the cell cycle coincides with maximum DNA production. Induction of reductase activity is prevented by cycloheximide. The enzyme requires dithiols for reduction of CDP ; it is not significantly stimulated by iron or magnesium ions nor dependent upon deoxyadenosylcobalamin. ATP stimulates the reaction but dATP or dTTP act as inhibitors. The ribonucleotide reductase of green algae differs from the B12-requiring enzyme characterized in . 相似文献
13.
A single subcutaneous injection of folate, homofolate or MTX resulted in the inhibition of the activity of dihydrofolate reductase in homogenates prepared from the kidneys of normal mice. Stimulation of 3H-thymidine uptake occurred in the kidneys of treated animals approximately 30 hr after administration of either folate or homofolate, and reached a peak 72 hr after administration. The effects of folate and MTX on dihydrofolate reductase activity were also determined. One hr after administration of 15 mg/kg methotrexate (MTX) or 300 mg/kg folate, enzyme activity was inhibited by 90%.3H-deoxyuridine uptake was neither stimulated nor depressed after treatment with MTX. After administration of folate, uptake of 3H-deoxyuridine was stimulated at approximately 30 hr after drug-treatment and reached a peak at 72 hr after folate administration. Treatment with xanthopterin had no effect on the activity of dihydrofolate reductase . Xanthopterin stimulated uptake of both deoxyuridine and thymidine in an identical manner.The increased DNA synthesis that occurs in animals after treatment with agents that cause renal damage is distinct from the effect these agents have upon dihydrofolate reductase. Nucleoside incorporation after treatment with folate, homofolate, MTX or xanthopterin cannot be predicted on the basis of enzyme inhibition. Treatment with MTX, folate or homofolate results in enzyme inhibition which is not correlated with the uptake of deoxyuridine into DNA. 相似文献
14.
Three phosphorylated dinucleosides designated HS1, HS2, and HS3, isolated from the water-mould , were shown to significantly inhibit ribonucleotide reductase activity from . All three compounds decreased CDP reduction in fungal extracts by 50% at concentrations of 0.1mM. At the same concentration HS3 also inhibited partially purified CDP reductase from Chinese hamster ovary cells by at least 80% but showed only 10% inhibition with enzyme from . ADP reductase activity from was inhibited 50% by both HS1 and HS3 at 0.1mM. HS2 however, showed no inhibitory effect on purine reduction. The levels of ribonucleotide reductase during the asexual growth cycle of correlated with thymidine uptake into DNA and with the synthesis of HS compounds. 相似文献
15.
Reconstitution of succinate-Q reductase is achieved by admixing soluble succinate dehydrogenase (SDH) and ubiquinone-protein-S (QP-S), a new protein isolated from the soluble cytochrome complex. The reconstituted reductase catalyzes reduction of Q by succinate. The reaction is fully sensitive to thenoyltrifluoroacetone. The reconstituted reductase (same as succinate-cytochrome reductase or submitochondrial particles) does not show “low concentration ferricyanide reductase activity” as soluble dehydrogenase does. In other words, this enzymic site on SDH is occupied by QP-S. When an artificial dye, such as phenazine methosulfate or Wurster's Blue, is used as electron acceptor the rate of oxidation of succinate by SDH is not significantly changed regardless of whether the dehydrogenase is in the free or in the reconstituted succinate-Q reductase forms. 相似文献
16.
The temperature dependence of drug monooxygenation in phenobarbital-induced rat liver microsomes has been investigated. With 7-ethoxycoumarin as a substrate the activity of the microsomes could be measured down to 0°C by the increase in fluorescence of the dealkylated reaction product 7-hydroxycoumarin (umbelliferone).Arrhenius plots of the activities at various temperatures between 0°C and 45°C showed a break in the activation energy around 20°C.Addition of deoxycholate or high concentrations of glycerol, known to solubilize membrane-bound enzymes, abolished the break of the activation energy. Cholesterol, incorporated into the microsomal membrane in amounts equimolar to the microsomal phospholipid content led to a decrease of the activation energy at low temperatures and to an increase at higher temperatures, resulting in a loss of the break.The activity of microsomal NADPH-cytochrome reductase with the water-soluble electron acceptor dichlorophenolindophenol showed no discontinuity in the Arrhenius plot. In addition the cumene hydroperoxide-mediated and cytochrome O-dealkylation of 7-ethoxycoumarin proceeded without a break in the activation energy.It is concluded that phospholipid phase transitions affect the electron transfer from the reductase to cytochrome . 相似文献
17.
When ) growing on glucose was starved for isoleucine by the addition of valine, the intracellular levels of fructose 6-phosphate, fructose 1,6-bisphosphate and dihydroxyacetone phosphate were abruptly decreased to one-half, but those of glucose 6-phosphate and ATP remained constant. In contrast, this was not the case with CP79(). Chloramphenicol released the response observed in CP78. These results suggest that the glycolytic activity is also under the stringent control. Since only glucosephosphate isomerase[EC 5.3.1.9] was significantly inhibited by guanosine 5′-diphosphate 3′-diphosphate among several glycolytic enzymes tested, the enzyme might be responsible for the decrease observed in CP78. 相似文献
18.
Ramli B. Mohd. Isa A.B. Sipat 《Biochemical and biophysical research communications》1982,108(1):206-212
The effect of the C-serum (the cytosol) on the activity of 3-hydroxy-3-methylglutaryl CoA reductase in the latex of was investigated. Depending on the clone from which the latex was obtained, the C-serum was found to depress or activate or have little effect on the enzyme activity. Boiling the C-serum however, resulted in a consistent activation effect in all the clones examined. Optimal activation was obtained with 20 μl boiled C-serum. Dialysis or EDTA (40 mM) treatment of the boiled C-serum did not diminish the activation effect. Although not essential, dithiothreitol complemented the activation effect of the boiled C-serum and the optimal concentration was 10 mM. Trypsin digestion of the boiled C-serum resulted in the complete loss of the activation effect. The activator in the boiled C-serum was salted out by ammonium sulphate at 25 – 100% saturation. Hevein had no effect on reductase activity. 相似文献
19.
Gordon A. Vehar James H. Freisheim 《Biochemical and biophysical research communications》1976,68(3):937-941
Reaction of dihydrofolate reductase from amethopterin-resistant with phenylglyoxal results in a complete loss of enzyme activity. This inactivation is concomitant with the modification of five of a total of eight arginine residues per mole of enzyme. In the presence of the reduced coenzyme, NADPH, two of the five reactive arginines are protected from chemical modification with complete retention of enzyme activity. The results suggest the involvement of essential arginine residues at or near the coenzyme binding site and thus at or near the active center of the enzyme. 相似文献
20.
Bengt Jernström Jorge Capdevila Sten Jakobsson Sten Orrenius 《Biochemical and biophysical research communications》1975,64(3):814-822
Cytochrome P-450 from rat lung microsomes has been solubilized and purified 8-fold by using affinity chromatography on an ω-amino--octyl derivative of Sepharose 4B. The purified fraction was free of cytochrome 5 and NADPH-cytochrome reductase and showed spectral characteristics similar to those of lung microsomal cytochrome P-450. When combined with NADPH-cytochrome reductase partially purified from liver microsomes, the cytochrome P-450 fraction supported the hydroxylation of benzo (α)pyrene and the activity was proportional to the content of the hemoprotein. No absolute requirement for phosphatidylcholine was found. 相似文献