Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CYTOCHROMES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15Linked to original sources
PubMed1987

Cytochrome b2, an electron carrier between flavocytochrome b2 and cytochrome c. Rapid kinetic characterization of the electron-transfer parameters with ionic-strength-dependence.

The oxidation-reduction properties of free cytochrome b2 isolated by controlled proteolysis from flavocytochrome b2, i.e. the flavodehydrogenase-bound cytochrome b2, were investigated by using stopped-flow spectrophotometry. The rapid kinetics of the reduction of cytochrome b2 by flavocytochrome b2 in the presence of L-lactate are reported. The self-exchange rate constant between reduced cytochrome b2 bound to the flavodehydrogenase and free cytochrome b2 was determined to be 10(5) M-1 X S-1 at 5 degrees C, I 0.2 and pH 7.0. The specific electron-transfer reaction between reduced cytochrome b2 and cytochrome c was also studied, giving an apparent second-order rate constant of 10(7) M-1 X S-1 at 5 degrees C, I 0.2 and pH 7.0. This electron-exchange rate is slightly modulated by ionic strength, following the Debye-Hückel relationship with a charge factor Z1Z2 = -1.9. Comparison of these data with those for the reduction of cytochrome c by flavodehydrogenase-bound cytochrome b2 [Capeillère-Blandin (1982) Eur. J. Biochem. 128, 533-542] leads to the conclusion that the intramolecular electron exchange between haem b2 and haem c within the reaction complex occurs at a rate very similar to that determined experimentally in presence of the flavodehydrogenase domain. The low reaction rate observed with free cytochrome b2 is ascribed to the low stability of the reaction complex formed between free cytochrome b2 and cytochrome c.

Cytochrome c Group↗
PubMed2004

Mitochondrial cytochrome c1 is a collapsed di-heme cytochrome.

Cytochrome c(1) from mitochondrial complex III and the di-heme cytochromes c in the corresponding enzyme from epsilon-proteobacteria have so far been considered to represent unrelated cytochromes. A missing link protein discovered in the genome of the hyperthermophilic bacterium Aquifex aeolicus, however, provides evidence for a close evolutionary relationship between these two cytochromes. The mono-heme cytochrome c(1) from A. aeolicus contains stretches of strong sequence homology toward the epsilon-proteobacterial di-heme cytochromes. These di-heme cytochromes are shown to belong to the cytochrome c(4) family. Mapping cytochrome c(1) onto the di-heme sequences and structures demonstrates that cytochrome c(1) results from a mutation-induced collapse of the di-heme cytochrome structure and provides an explanation for its uncommon structural features. The appearance of cytochrome c(1) thus represents an extension of the biological protein repertoire quite different from the widespread innovation by gene duplication and subsequent diversification.

Amino Acid Sequence↗
PubMed1988

Characterization of human neutrophil leukotriene B4 omega-hydroxylase as a system involving a unique cytochrome P-450 and NADPH-cytochrome P-450 reductase.

Leukotriene B4 (LTB4), a potent chemotactic agent, was catabolized to 20-hydroxyleukotriene B4 (20-OH-LTB4) by the 150,000 x g pellet (microsomal fraction) of human neutrophil sonicate. The reaction required molecular oxygen and NADPH, and was significantly inhibited by carbon monoxide, suggesting that a cytochrome P-450 is involved. The neutrophil microsomal fraction showed a carbon monoxide difference spectrum with a peak at 450 nm in the presence of NADPH or dithionite, indicating the presence of a cytochrome P-450. The addition of LTB4 to the microsomal fraction gave a type-I spectral change with a peak at around 390 nm and a trough at 422 nm, indicating a direct interaction of LTB4 with the cytochrome P-450. The dissociation constant of LTB4, determined from the difference spectra, is 0.40 microM, in agreement with the kinetically determined apparent Km value for LTB4 (0.30 microM). Such a spectral change was not observed with prostaglandins A1, E1 and F2 alpha or lauric acid, none of which inhibited the LTB4 omega-hydroxylation. The inhibition of the LTB4 omega-hydroxylation by carbon monoxide was effectively reversed by irradiation with monochromatic light of 450 nm wavelength. The photochemical action spectrum of the light reversal of the inhibition corresponded remarkably well with the carbon monoxide difference spectrum. These observations provide direct evidence that the oxygen-activating component of the LTB4 omega-hydroxylase system is a cytochrome P-450. Ferricytochrome c inhibited the hydroxylation of LTB4 and the inhibition was fortified by cytochrome oxidase. An antibody raised against rat liver NADPH-cytochrome-P-450 reductase inhibited both LTB4 omega-hydroxylase activity and the NADPH-cytochrome-c reductase activity of human neutrophil microsomal fraction. These observations indicate that NADPH-cytochrome-P-450 reductase acts as an electron carrier in LTB4 omega-hydroxylase. On the other hand, an antibody raised against rat liver microsomal cytochrome b5 inhibited the NADH-cytochrome-c reductase activity but not the LTB4 omega-hydroxylase activity of human neutrophil microsomal fraction, suggesting that cytochrome b5 does not participate in the LTB4-hydroxylating system. These characteristics indicate that the isoenzyme of cytochrome P-450 in human neutrophils, LTB4 omega-hydroxylase, is different from the ones reported to be involved in omega-hydroxylation reactions of prostaglandins and fatty acids.

Carbon Monoxide↗
PubMed2000

Modulation of cytochrome P-450 dependent monooxygenases in streptozotocin-induced diabetic hamster: I. Effects of propofol on defluorination and cytochrome P-450 activities.

BACKGROUND: Diabetes mellitus could induce polymorphic alterations of metabolic activities of cytochrome P-450 dependent monooxygenases in chemical-induced diabetic animals. The purpose of this study is to define the functional impact of clinical concentrations of propofol on the metabolic activities of cytochrome P-450 in the diabetic animals. METHODS: In order to validate the effect of propofol on cytochrome P-450 activities, especially the cytochrome P-450 2E1 and its defluorination activity, we applied NADPH-generating system to measure the metabolizing activities of cytochrome P-450 isozymes of streptozotocin-induced diabetic hamsters within the microsomes preincubated with various concentrations of propofol. The extent of defluorination and activity of cytochrome P-450 2E1 were assessed by reacting the propofol-treated microsomes in NADPH-generating system with enflurane and aniline as substrates respectively. Drug metabolizing activities of cytochrome 1A1, 2B1, and 3A4 were evaluated by metabolizing specific substrates, benzo(a)pyrene, pentoxyresorufin and erythromycin, within the microsomes of diabetic hamsters preincubated with various concentrations of propofol. RESULTS: The hepatic and renal defluorination of enflurane was significantly inhibited by 0.05 and 0.10 mM propofol in the microsomes of diabetic hamster (P < 0.05). The activities of aniline hydroxylase (cytochrome 2E1), pentoxyresorufin O-dealkylase (cytochrome 2B1) and benzo(a)pyrene hydroxylase (cytochrome 1A1) were inhibited by propofol in a concentration-dependent manner from 0.05 to 0.10 mM. However, propofol showed no significant effect to the erythromycin N-demethylase (cytochrome 3A4) at its concentration of 0.05-0.10 mM in the diabetic hamsters. CONCLUSIONS: Our data demonstrated that propofol in therapeutic concentrations of 0.05 and 0.10 mM, could inhibit both liver and kidney defluorination and cytochrome P-450's activities of the diabetic hamsters in vitro of different extent. This should remind clinicians of propofol's potential drug-to-drug interactions in the diabetic patients.

Animals↗
PubMed1989

A ubiquinone derivative that inhibits mitochondrial cytochrome b-c1 complex but not chloroplast cytochrome b6-f complex activity.

A ubiquinone derivative, 3-chloro-5-hydroxyl-2-methyl-6-decyl- 1,4-benzoquinone (3-CHMDB), which shows different effects on the mitochondrial cytochrome b-c1 complex and chloroplast cytochrome b6-f complex, has been synthesized and characterized. When the cytochrome b-c1 complex is treated with varying concentrations of 3-CHMDB and assayed at constant substrate (Q2H2) concentration, a 50% inhibition is observed when 2 mol of 3-CHMDB per mol of enzyme are used. The degree of inhibition is dependent on the substrate concentration. When ubiquinol-cytochrome c reductase is treated with 2 mol of 3-CHMDB per mol of enzyme, less inhibition is observed with a lower substrate concentration, suggesting the possible existence of two forms of reductases: one with a high affinity for ubiquinone and another with a low affinity. 2-Chloro-5-hydroxyl-3-methyl-6-decyl-1,4-benzoquinone (2-CHMDB), an isomer of 3-CHMDB, shows much less inhibition of the mitochondrial cytochrome b-c1 complex, suggesting that the quinone binding site in this complex is highly specific. In contrast to the inhibition observed with the cytochrome b-c1 complex, 3-CHMDB causes no inhibition of the plastoquinol-plastocyanin reductase activity of chloroplast cytochrome b6-f complex, regardless of whether plastoquinol-2 or ubiquinol-2 is used as substrate. 3-CHMDB restores the dibromothymoquinone-altered EPR spectra of iron-sulfur protein in both complexes. In the case of the cytochrome b6-f complex, 3-CHMDB also partially restores the dibromothymoquinone-inhibited activity. Reduced form 3- or 2-CHMDB is oxidizable by the cytochrome b6-f complex, but not by the cytochrome b-c1 complex. These results suggest that the quinol oxidizing sites in the cytochrome b6-f complex may differ from those in the mitochondrial cytochrome b-c1 complex.

Binding Sites↗
PubMed1989

Biogenesis of cytochrome c1. Role of cytochrome c1 heme lyase and of the two proteolytic processing steps during import into mitochondria.

The biogenesis of cytochrome c1 involves a number of steps including: synthesis as a precursor with a bipartite signal sequence, transfer across the outer and inner mitochondrial membranes, removal of the first part of the presequence in the matrix, reexport to the outer surface of the inner membrane, covalent addition of heme, and removal of the remainder of the presequence. In this report we have focused on the steps of heme addition, catalyzed by cytochrome c1 heme lyase, and of proteolytic processing during cytochrome c1 import into mitochondria. Following translocation from the matrix side to the intermembrane-space side of the inner membrane, apocytochrome c1 forms a complex with cytochrome c1 heme lyase, and then holocytochrome c1 formation occurs. Holocytochrome c1 formation can also be observed in detergent-solubilized preparations of mitochondria, but only after apocytochrome c1 has first interacted with cytochrome c1 heme lyase to produce this complex. Heme linkage takes place on the intermembrane-space side of the inner mitochondrial membrane and is dependent on NADH plus a cytosolic cofactor that can be replaced by flavin nucleotides. NADH and FMN appear to be necessary for reduction of heme prior to its linkage to apocytochrome c1. The second proteolytic processing of cytochrome c1 does not take place unless the covalent linkage of heme to apocytochrome c1 precedes it. On the other hand, the cytochrome c1 heme lyase reaction itself does not require that processing of the cytochrome c1 precursor to intermediate size cytochrome c1 takes place first. In conclusion, cytochrome c1 heme lyase catalyzes an essential step in the import pathway of cytochrome c1, but it is not involved in the transmembrane movement of the precursor polypeptide. This is in contrast to the case for cytochrome c in which heme addition is coupled to its transport directly across the outer membrane into the intermembrane space.

Chromatography, High Pressure Liquid↗
PubMed1984

An inhibitor of mitochondrial respiration which binds to cytochrome b and displaces quinone from the iron-sulfur protein of the cytochrome bc1 complex.

Myxothiazol, an antibiotic from Myxococcus fulvus, which inhibits mitochondrial respiration in the bc1 complex of the respiratory chain, has effects on the redox components of isolated succinate-cytochrome c reductase complex which suggest that it interacts with both cytochrome b and the iron-sulfur protein of the bc1 complex. The inhibitor appears to increase the midpoint potentials of cytochromes b-562 and b-566, as indicated by an increase in their reducibility by the succinate/fumarate couple. It also causes a red shift in the optical spectrum of ferrocytochrome b-566, as reported previously (Becker, W. F., Von Jagow , G., Anke , T., Steglisch , W. (1981) FEBS Lett. 132, 329-333). This red shift is enhanced by Triton X-100, and there is no shift in the spectrum of b-562. These results are consistent with evidence that mutations conferring myxothiazol resistance in yeast map to the mitochondrial gene for cytochrome b ( Thierbach , G., and Michaelis, G. (1982) Mol. Gen. Genet. 186, 501-506). In addition, myxothiazol has effects on reduction of the cytochromes b and c1 by succinate or ubiquinol which are identical to those caused by removal of the iron-sulfur protein from the bc1 complex. It blocks reduction of cytochrome c1 during single and multiple turnovers of the bc1 complex, but does not block reduction of the b cytochromes. In the presence of antimycin, it blocks reduction of both cytochromes b and c1. In contrast to antimycin, myxothiazol inhibits oxidant-induced reduction of both b cytochromes and does not inhibit their oxidation by fumarate. Myxothiazol also inhibits reduction of the iron-sulfur protein by ubiquinol and shifts the gx resonance in the EPR spectrum of the iron-sulfur protein from g = 1.79 to 1.76. It does not affect the midpoint potential of the iron-sulfur protein, but does eliminate the increase in midpoint potential which is caused by inhibitory hydroxyquinones which bind to the iron-sulfur protein. The effects of myxothiazol are consistent with a protonmotive Q cycle pathway of electron transfer in which myxothiazol binds to cytochrome b and displaces quinone from the iron-sulfur protein of the bc1 complex. These results suggest either that a myxothiazol-induced conformational change in cytochrome b is transmitted to a quinone binding site on the iron-sulfur protein, or that there is a quinone binding site which consists of peptide domains from both cytochrome b and iron-sulfur protein.

Animals↗
PubMed1983

A high spin form of cytochrome P-448 highly purified from PCB-treated rats--II. Characteristic requirement of cytochrome b5 for maximum activity.

A high spin form of cytochrome P-448 (PCB P-448-H), highly purified from microsomes of PCB-treated rats, catalyzed oxidations of several compounds and required cytochrome b5 for its full activities in all oxidations examined. PCB P-448-H catalyzed the hydroxylation of aniline and O-dealkylations of p-alkoxy derivatives of aniline and nitrobenzene and 7-alkoxy derivatives of coumarin. Among the activities measured, hydroxylation of aniline and O-dealkylation of p-alkoxy derivatives of aniline were catalyzed by PCB P-448-H more efficiently than by PCB P-448-L, which was a low spin form of cytochrome P-448 purified from liver microsomes of PCB-treated rats. In all reactions, PCB P-448-H required cytochrome b5 for maximum activity. Slight requirements were also seen with PCB P-448-L but varied equivocally depending on the substrates. Cytochrome b5 showed its maximum effects on p-propoxyaniline O-depropylation activity at a molar ratio of cytochrome b5 to PCB P-448-H of 1:2. The enhancement by cytochrome b5 was more pronounced when lower concentrations of either the substrate or NADPH-cytochrome P-450 reductase were added to the reconstituted system. Based on these results, we confirm that PCB P-448-H is a unique form of cytochrome P-448 with respect to the requirements for cytochrome b5 and is a good probe to study the mechanisms involved in the enhancement of drug oxidations by cytochrome b5.

Animals↗
PubMed2001

Electron transfer and stability of the cytochrome b6f complex in a small domain deletion mutant of cytochrome f.

The lumen segment of cytochrome f consists of a small and a large domain. The role of the small domain in the biogenesis and stability of the cytochrome b(6)f complex and electron transfer through the cytochrome b(6)f complex was studied with a small domain deletion mutant in Chlamydomonas reinhardtii. The mutant is able to grow photoautotrophically but with a slower rate than the wild type strain. The heme group is covalently attached to the polypeptide, and the visible absorption spectrum of the mutant protein is identical to that of the native protein. The kinetics of electron transfer in the mutant were measured by flash kinetic spectroscopy. Our results show that the rate for the oxidation of cytochrome f was unchanged (t(12) = approximately 100 micros), but the half-time for the reduction of cytochrome f is increased (t(12) = 32 ms; for wild type, t(12) = 2.1 ms). Cytochrome b(6) reduction was slower than that of the wild type by a factor of approximately 2 (t(12) = 8.6 ms; for wild type, t(12) = 4.7 ms); the slow phase of the electrochromic band shift also displayed a slower kinetics (t(12) = 5.5 ms; for wild type, t(12) = 2.7 ms). The stability of the cytochrome b(6)f complex in the mutant was examined by following the kinetics of the degradation of the individual subunits after inhibiting protein synthesis in the chloroplast. The results indicate that the cytochrome b(6)f complex in the small domain deletion mutant is less stable than in the wild type. We conclude that the small domain is not essential for the biogenesis of cytochrome f and the cytochrome b(6)f complex. However, it does have a role in electron transfer through the cytochrome b(6)f complex and contributes to the stability of the complex.

Animals↗