Antitumor agents. I. Effect of 5-fluorouracil and cyclophosphamide on liver microsomes and thymus of rat.
Effects of antitumor agents on rat liver microsomal drug-metabolizing enzyme activities and thymus lymphocytes were studied in male Wistar rats. High doses of 5-fluorouracil (5-FU) and cyclophosphamide (CP) given parenterally for 6 days caused a partial decrease in whole body weight and the microsomal enzyme content such as cytochrome P-450 and cytochrome b5. Aniline p-hydroxylase and aminopyrine N-demethylase activities also decreased in rats dosed for 5 days decreased compared with the control. Both compounds in the high concentrations produced spectral change of "modified type II". However, the magnitude of the spectral changes observed was independent of the the concentration of substrate added. The addition of NADPH to the microsomes-substrate mixture modified the spectral change. Both drugs caused a considerable decrease in thymus weight and the number of thymus lymphocytes, while the alkaline phosphatase activity was enhanced in 5-FU groups, indicating that the agents cause a significant involution of the thymus. Decrease in the total number of the lymphocytes was greater than that in the blood leucocytes. (+info
Balanced regulation of expression of the gene for cytochrome cM and that of genes for plastocyanin and cytochrome c6 in Synechocystis.
The cytM gene for cytochrome cM was previously found in Synechocystis sp. PCC 6803. Northern blotting analysis revealed that the cytM gene was scarcely expressed under normal growth conditions but its expression was enhanced when cells were exposed to low temperature or high-intensity light. By contrast, the expression of the genes for cytochrome c6 and plastocyanin was suppressed at low temperature or under high-intensity light. These observations suggest that plastocyanin and/or cytochrome c6, which are dominant under non-stressed conditions, are replaced by cytochrome cM under the stress conditions. (+info
Comparison of effects of acetaminophen on liver microsomal drug metabolism and lipid peroxidation in rats and mice.
Studies were conducted to determine the in vivo effect of acetaminophen (AAP) on the lipid peroxidation, drug metabolizing enzyme activity and microsomal electron transfer system of rat and mouse liver. AAP was found to inhibit ethylmorphine N-demethylase activity in the presence of NADPH and this inhibition of the enzyme was due to decrease in cytochrome P-450 content, but not due to change in lipid peroxidation in liver microsomes. Kinetical data showed that AAP administration had no effect on Km values of ethylmorphine N-demethylase, however, a decrease in the Vmax values was seen in rats and mice. There was no significant effect of AAP on both NADPH-cytochrome c reductase and the content of cytochrome b5 3 hours after this administration to rats and mice. On the other hand, AAP induced a significant decrease in NADH-ferricyanide reductase in mice, but not in rats. The greatest decrease in cytochrome P-450 observed among the components of the liver microsomal electron transfer system of rats and mice. (+info
Formation in isolated rat liver microsomes and nuclei of benzo(a)pyrene metabolites that bind to DNA.
The hepatic nuclear fraction isolated from 3-methylcholanthrene (MC)-treated rats contained enhanced levels of cytochrome P-450 and aryl hydrocarbon hydroxylase [benzo(a)pyrene (BP) monooxygenase], whereas the activities of epoxide hydrase and reduced nicotinamide adenine dinucleotide phosphate-cytochrome c reductase and the concentration of cytochrome b5 were not altered. The metabolite pattern of BP was investigated by using high-pressure liquid chromatography and was found to be similar in nuclei and microsomes from MC-treated rats. After incubation of the nuclear fraction with [3H]BP and reduced nicotinamide adenine dinculeotide phosphate, radioactivity was found to be associated with nuclear DNA and the extent of binding was markedly enhanced by pretreatment of the animals with MC. Binding was strongly inhibited by a-napthoflavone but was not influenced by 1,1,1-trichloropropene-2,3-oxide, an inhibitor of epoxide hydrase. In the presence of microsomes from MC-treated rats, increased binding of BP to DNA was observed in nuclei from both control and MC-treated rats; moreover, when the nuclear DNA was replaced by a corresponding amount of calf thymus DNA, the extent of binding was severalfold enhanced. In contrast to nuclei from control rats, the nuclear fraction from MC-treated rats showed an increase in bound radioactivity when incubated with a microsome-free supernatant, obtained by incubating microsomes from MC-treated rats with [3H]BP. The increase in extent of binding was eliminated in the presence of menadione or alpha-naphthoflavone. It is suggested that under the conditions used here the following different processes may have contributed to the total incorporation of BP products into nuclear DNA: (a) formation of DNA-binding products derived from BP by nuclear aryl hydrocarbon hydroxylase; (b) formation of DNA-binding products from microsomal BP metabolites by nuclear aryl hydrocarbon hydroxylase; and (c) direct transfer of reactive microsomal metabolites to nuclear DNA. (+info
Q-Band resonance Raman investigation of turnip cytochrome f and Rhodobacter capsulatus cytochrome c1.
The results of a comprehensive Q-band resonance Raman investigation of cytochrome c1 and cytochrome f subunits of bc1 and b6f complexes are presented. Q-band excitation provides a particularly effective probe of the local heme environments of these species. The effects of protein conformation (particularly axial ligation) on heme structure and function were further investigated by comparison of spectra obtained from native subunits to those of a site directed c1 mutant (M183L) and various pH-dependent species of horse heart cytochrome c. In general, all species examined displayed variability in their axial amino acid ligation that suggests a good deal of flexibility in their hemepocket conformations. Surprisingly, the large scale protein rearrangements that accompany axial ligand replacement have little or no effect on macrocycle geometry in these species. This indicates the identity and/or conformation of the peptide linkage between the two cysteines that are covalently linked to the heme periphery may determine heme geometry. (+info
Light-induced oxidation-reduction reactions of cytochromes in the green sulfur photosynthetic bacterium Prosthecochloris aesturarii.
The light-induced oxidation-reduction reactions of cytochromes in intact cells, starved cells, and chlorobium vesicle fractions of the green sulfur photosynthetic bacterium Prosthecochloris aesturarii were studied under anaerobic conditions. On the basis of both kinetic and spectral properties, at least three cytochrome species were found to be involved in the light-induced oxidation-reduction reactions of intact cells. These cytochromes were designated according to the positions of alpha-band maxima as C555 (rapid and slow components) and C552 (intermediate). By comparing the light-minus-dark difference spectra with the reduced-minus-oxidized difference spectra of purified cytochromes of this organism, rapid component C555 and intermediate component C552 are suggested to correspond to the purified cytochromes c-555(550) and c-551.5, respectively. Although the identity of the slow-phase component is uncertain, one possibility is that the slow phase is due to the bound form of c-555(550). In substrate-depleted (starved) cells, only one cytochrome species, C555 remained in the reduced state in the dark and oxidized upon actinic illumination. This corresponds to the rapid C555 component in intact cells. In the case of chlorobium vesicle fractions, one cytochrome species having an alpha-band maximum at 554 nm was oxidized by actinic light. The effects of several inhibitors on the absorbance changes of intact cells were studied. Antimycin A decreased the rate of the dark reduction of rapid C555 component. The complex effects of CCCP (carbonyl cyanide m-chlorophenylhydrazone) on the oxidation-reduction reactions of cytochromes were interpreted as the results of inhibition of the electron donation to oxidized C552 and C555 (slow), and a shift of the dark steady-state redox levels of cytochromes. Based on these findings, it is suggested that the rapid C555 component is located in a cyclic electron transfer pathway. The other two cytochromes, C552 and C555 (slow), may be located in non-cyclic electron transfer pathways and receive electrons from exogenous substrates such as sodium sulfide. A tentative scheme for the electron transfer system in Prosthecochloris aestuarii is presented and its nature is discussed. (+info
Tolterodine does not affect the human in vivo metabolism of the probe drugs caffeine, debrisoquine and omeprazole.
AIM: To investigate the in vivo effect of treatment with tolterodine on debrisoquine 4-hydroxylation (an index of CYP2D6 activity), omeprazole 5-hydroxylation (CYP2C19), omeprazole sulphoxidation (CYP3A4) and caffeine N3-demethylation (CYP1A2). METHODS: Twelve healthy male volunteers (eight extensive metabolisers [EMs] and four poor metabolisers [PMs] with respect to CYP2D6) received 4 mg tolterodine L-tartrate orally twice daily for 6 days. All subjects were EMs with respect to CYP2C19. The subjects received single oral doses of debrisoquine (10 mg), omeprazole (20 mg) and caffeine (100 mg) for determination of the appropriate metabolic ratios (MR). The drugs were given on separate consecutive days, before, during and after the co-administration of tolterodine. RESULTS: Mean serum tolterodine concentrations were 5-10 times higher in PMs than in EMs. Serum concentrations of the active 5-hydroxymethyl metabolite of tolterodine, 5-HM, were not quantifiable in PMs. The mean MR of debrisoquine (95% confidence interval) during tolterodine treatment was 0.50 (0.25-0.99) and did not differ statistically from the values before [0.49 (0.20-1.2)] and after tolterodine administration [0.46 (0.14-1.6)] in EMs. The mean MR of omeprazole hydroxylation and sulphoxidation or caffeine metabolism were not changed in the presence of tolterodine in either EMs or PMs. Debrisoquine and caffeine had no significant effect on the AUC(1,3 h) of either tolterodine or 5-HM, but during omeprazole administration small decreases (13-19%) in these parameters were seen. CONCLUSIONS: Tolterodine, administered at twice the expected therapeutic dosage, did not change the disposition of the probe drugs debrisoquine, omeprazole and caffeine and thus had no detectable effect on the activities of CYPs 2D6, 2C19, 3A4 and 1A2. Alteration of the metabolism of substrates of these enzymes by tolterodine is unlikely to occur. (+info
A new cytochrome subunit bound to the photosynthetic reaction center in the purple bacterium, Rhodovulum sulfidophilum.
The nucleotide sequence of the puf operon, which contains the genes encoding the B870 light-harvesting protein and the reaction center complex of the purple photosynthetic bacterium, Rhodovulum sulfidophilum, was determined. The operon, which consisted of six genes, pufQ, pufB, pufA, pufL, pufM, and pufC, is a new variety in photosynthetic bacteria in the sense that pufQ and pufC coexist. The amino acid sequence of the cytochrome subunit of the reaction center deduced from the pufC sequence revealed that this cytochrome contains only three possible heme-binding motifs; the heme-1-binding motif of the corresponding tetraheme cytochrome subunits was not present. This is the first exception of the "tetraheme" cytochrome family in purple bacteria and green filamentous bacteria. The pufC sequence also revealed that the sixth axial ligands to heme-1 and heme-2 irons were not present in the cytochrome either. This cytochrome was actually detected in membrane preparation as a 43-kDa protein and shown to associate functionally with the photosynthetic reaction center as the immediate electron donor to the photo-oxidized special pair of bacteriochlorophyll. This new cytochrome should be useful for studies on the role of each heme in the cytochrome subunit of the bacterial reaction center and the evolution of proteins in photosynthetic electron transfer systems. (+info