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At least 937 records · Page 52Linked to original sources
PubMed1987

NMR study of the interaction between cytochrome b5 and cytochrome c. Observation of a ternary complex formed by the two proteins and [Cr(en)3]3+.

The interaction between horse cytochrome c and the tryptic fragment of bovine liver microsomal cytochrome b5 in the absence and presence of [Cr(ethylenediamine)3]Cl3 was studied by 1H NMR spectroscopy. The protein-protein interaction region on cytochrome b5 was found to be different from the [Cr(en)3]3+-binding region. The solvent-exposed propionate-bearing edge of the haem of cytochrome b5 is accessible to [Cr(en)3]3+ in the interprotein complex.

Animals↗
PubMed1993

NADH-cytochrome b5 reductase and cytochrome b5 isoforms as models for the study of post-translational targeting to the endoplasmic reticulum.

Cytochrome b5 and NADH-cytochrome b5 reductase are integral membrane proteins with cytosolic active domains and short membrane anchors, which are inserted post-translationally into their target membranes. Both are produced as different isoforms, with different localizations, in mammalian cells. In the rat, the reductase gene generates two transcripts by an alternative promoter mechanism: a ubiquitous mRNA coding for the myristylated membrane-bound form, and an erythroid mRNA which generates both the soluble form and a nonmyristylated membrane-binding form. The available evidence indicates that the ubiquitous myristylated form binds to the cytosolic face of both outer mitochondrial membranes and ER. In contrast, two genes code for two homologous forms of cytochrome b5, one of which is found on outer mitochondrial membranes, the other on the ER. The gene specifying the ER form probably also generates an erythroid-specific mRNA by alternative splicing, which codes for soluble cytochrome b5. Possible molecular mechanisms responsible for the observed localizations of these different enzyme isoforms are discussed.

Animals↗
PubMed1987

Primary structure of the bc1 complex of Rhodopseudomonas capsulata. Nucleotide sequence of the pet operon encoding the Rieske cytochrome b, and cytochrome c1 apoproteins.

The nucleotide sequence of the pet operon of Rhodopseudomonas capsulata strain SB1003 has been determined. This operon consists of the petA, petB and petC genes, which encode the Rieske Fe-S protein, cytochrome b and cytochrome c1, respectively, all components of the ubiquinol-cytochrome c2 oxidoreductase. The deduced amino acid sequences of the pet genes show homology to the corresponding proteins from other organisms, and particularly high homologies (over 90% for amino acid and nucleotide sequences) to the previously described fbc operon from a strain previously identified as Rhodopseudomonas spheroides GA. The amino acid sequences of the pet proteins are discussed with reference to the structure and function of the ubiquinol-cytochrome c2 oxidoreductase.

Amino Acid Sequence↗
PubMed1999

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.

Bacterial Proteins↗
PubMed1988

Effects of amino acid replacements in yeast iso-1 cytochrome c on heme accessibility and intracomplex electron transfer in complexes with cytochrome c peroxidase.

The kinetics of reduction of wild type and several site-specific mutants of yeast iso-1 cytochrome c (Arg-13----Ile, Gln-16----Ser, Gln-16----Lys, Lys-27----Gln, Lys-72----Asp), both free and in 1:1 complexes with yeast cytochrome c peroxidase, by free flavin semiquinones have been studied. Intramolecular one-electron transfer from the ferrous cytochromes c to the H2O2-oxidized peroxidase at both low (8 mM) and high (275 mM) ionic strengths was also studied. The accessibility of the cytochrome c heme within the electrostatically stabilized complex and the rate constants for intramolecular electron transfer at both low and high ionic strength are highly dependent on the specific amino acids present at the protein-protein interface. Importantly, replacement by uncharged amino acids of Arg or Lys residues thought to be important in orientation and/or stabilization of the electron-transfer complex resulted in increased rates of electron transfer. In all cases, an increase in ionic strengths from 8 to 275 mM also produced increased intramolecular electron-transfer rate constants. The results suggest that the electrostatically stabilized 1:1 complex is not optimized for electron transfer and that by neutralization of key positively charged residues, or by an increase in the ionic strength thereby masking the ionic interactions, the two proteins can orient themselves to allow the formation of a more efficient electron-transfer complex.

Amino Acids↗
PubMed1990

Cytochrome c oxidase: decay of the primary oxygen intermediate involves direct electron transfer from cytochrome a.

The decay of the primary intermediate generated in the reaction of oxygen with cytochrome c oxidase is nearly one order of magnitude faster in the fully reduced form of the enzyme than it is in the mixed valence form. To account for this observation, we propose a model describing the early molecular events in the reaction. In this model the decay of the primary Fe-O2 intermediate in the fully reduced enzyme is a consequence of direct electron transfer from cytochrome a. To test the model we measured the time dependence of the oxidation of cytochrome a by monitoring the resonance Raman scattering intensity of its vibrational modes. A rapid oxidation of cytochrome a was detected that quantitatively agrees with the model. These results indicate that the mechanism of oxygen reduction and proposed frameworks for proton translocation must be reexamined.

Animals↗
PubMed1997

NADPH-cytochrome P-450 reductase, cytochrome P-450 2C11 and P-450 1A1, and the aryl hydrocarbon receptor in livers of rats fed methyl-folate-deficient diets.

We investigated three hepatic cytochrome P-450 isozymes and the aryl hydrocarbon (Ah) receptor in rats fed one of the following three diets for 15 months: a diet containing the AIN vitamin mixture (control), the control diet devoid of choline and folate (CFD), or the CFD diet devoid of niacin (CFND). Hepatic tumors developed in all CFD- and CFND-fed rats. Western blot analyses of nontumor hepatic tissue showed that NADPH-cytochrome P-450 reductase (P-450 reductase) increased significantly in the CFD and CFND groups compared with the control group. Hepatic cytochrome P-450 2C11 (CYP2C11) was not detectable in the CFD and CFND groups compared with the control group. Ah receptor and cytochrome P-450 1A1 (CYP1A1) were detected in higher amounts in livers of both deficient groups. CYP1A1 is an enzyme associated with bioactivation of exogenous genotoxins. To our knowledge, this is the first time it has been shown that CYP1A1 and the Ah receptor are induced by dietary deficiencies.

Animals↗
PubMed1981

Effect of bran and citrus pulp on hepatic, small intestinal and colonic HMG CoA reductase, cytochrome P450 and cytochrome b5 levels in rats.

The effect of dietary wheat bran and citrus pulp on hepatic, small intestinal and colonic HMG-CoA reductase activity, cytochrome P450 and cytochrome b5 levels was studied in F344 rats. Colonic and small intestinal HMG-CoA reductase activity was significantly lower in the wheat bran group than the control group. No differences in hepatic HMG-CoA reductase activity occurred between the wheat bran, citrus pulp and control groups. A direct relationship between hepatic cholesterol levels and hepatic Cytochrome P450 levels was demonstrated. A similar trend was exhibited between fecal cholesterol and colonic cytochrome P450 levels in the colon. These results suggest that the effect of certain types of dietary fiber in small intestinal and colonic cholesterogenesis is mediated through alterations in small intestinal and colonic mixed function oxidase activity.

Animals↗
PubMed1986

Nucleotide sequence and transcription of the fbc operon from Rhodopseudomonas sphaeroides. Evaluation of the deduced amino acid sequences of the FeS protein, cytochrome b and cytochrome c1.

The fbc operon from Rhodopseudomonas sphaeroides encodes the three redox carriers of the ubiquinol-cytochrome-c reductase (b/c1 complex): FeS protein, cytochrome b and cytochrome c1 [Gabellini, N. et al. (1985) EMBO J.2, 549-553]. The nucleotide sequence of 3874 bp of cloned R. sphaeroides chromosomal DNA, including the three structural genes fbcF, fbcB and fbcC has been determined. The reading frames of the fbc genes could be identified readily since the encoded amino acid sequences are highly homologous with the sequences of the corresponding mitochondrial polypeptides. Initiation and termination points for transcription have been investigated by S1 nuclease protection analysis. The transcription of the fbc operon starts approximately 240 base pairs upstream from the start codon of the fbcF gene and terminates 120 base pairs downstream from the stop codon of the fbcC gene. Nucleotide sequences resembling recognition signals for the binding and release of the RNA polymerase were identified. The N-terminal amino acid sequence of the mature cytochrome c1 was obtained by automated Edman degradation of the isolated subunit, confirming the fbcC reading frame and indicating that the bacterial preapocytochrome c1 has a transient leader sequence including 21 residues. The N-terminal sequence of one hydrophilic peptide of the FeS protein has been also obtained confirming the fbcF reading frame. The deduced amino acid sequences are discussed in relation to the known primary structures of the homologous proteins from mitochondria and chloroplasts. The primary structures of the polypeptides are evaluated with respect to their topology in the membrane, their biogenesis, the structure of the catalytic sites and subunit interactions.

Amino Acid Sequence↗
PubMed1987

Effect of autoxidized linoleic acid on the contents of cytochrome P-450 and cytochrome b5, and drug-metabolizing enzyme activities in rat liver.

Autoxidized linoleic acid (AL) having 800 meq/kg of peroxide value and 1,700 meq/kg of carbonyl value was given in repeated oral doses for 1-15 days at a daily dose of 2.5 ml/kg to male Wistar rats. During the administration, the effect of AL on drug-metabolizing activity was investigated periodically in liver microsomes. The contents of cytochrome P-450 and b5 were increased by consecutive oral doses for 3-7 days. Thereafter, the amount of cytochrome P-450 decreased gradually, but the b5 decreased slightly. Thus, after administration for 11-15 days, the cytochrome P-450 content was significantly lower but the cytochrome b5 content was rather high in comparison with the control group. The aminopyrine-N-demethylase activity was not reduced even after repeated oral doses of AL for 15 days. The activation of 2-acetyl amino fluorene (2-AAF), which the authors termed S-9 activity, gradually decreased during administration for more than 3 days, and completely disappeared after administration for 9 days.

2-Acetylaminofluorene↗
PubMed1992

Characterization of lysyl residues of NADH-cytochrome b5 reductase implicated in charge-pairing with active-site carboxyl residues of cytochrome b5 by site-directed mutagenesis of an expression vector for the flavoprotein.

An expression vector for bovine NADH-cytochrome b5 reductase was constructed from two DNA fragments that were derived from beef liver poly(A+) RNA using the polymerase chain reaction. Site-directed mutagenesis of the 3 lysine residues of the reductase, previously implicated in the formation of active-site charge pairs with carboxylate residues of cytochrome b5, was then used to obtain the purified catalytic domains of flavoproteins modified at each of these sites. The observed marked decreases in catalytic efficiencies of substitutions of a negative charge at the normally positively charged residues with the catalytic domain of cytochrome b5 are consistent with their participation in the formation of charge pairs with carboxylate groups of the hemeprotein to optimize rapid electron transfer from the reductase flavin to the heme of the cytochrome.

Amino Acid Sequence↗
PubMed1990

Characterization of the covalent cross-links of the active sites of amidinated cytochrome b5 and NADH:cytochrome b5 reductase.

Preparations of amidinated cytochrome b5 and cytochrome b5 reductase, cross-linked by using a soluble carbodiimide to promote the formation of covalent bonds between carboxyl groups of the hemeprotein and nucleophilic residues of the flavoprotein at the surfaces involved in protein-protein contacts during electron transfer, have been used to characterize the charge pair interactions that occur during electron transfer between the free proteins. Sequence analyses of tryptic, V8 protease-, and Asp-N protease-generated peptides show that the heme propionyl carboxyl group at the surface of the cytochrome forms an ester bond with Ser162 of the reductase, thus implicating Lys163 as the normal participant in ionic bonding between the active sites of the two proteins. Moreover, Lys41 and Lys125 directly form amide bonds with carboxyl residues on the active-site surface of the cytochrome. In the case of Lys41, this involves Glu52 and/or Glu60, and Glu47 and/or Glu48 for Lys125, again implicating these residues as the groups that form charge pairs during normal interactions between the active sites of the two proteins.

Amides↗
PubMedDate not supplied

Influence of cytochrome b5 on the stoichiometry of the different oxidative reactions catalyzed by liver microsomal cytochrome P-450.

Stoichiometries of oxygen and NADPH consumption and product and hydrogen peroxide formation are examined for three forms of cytochrome P-450, LM2, RLM2, and RLM5, using several different substrates. As reported earlier, during the metabolism of some substrates [Gorsky, Koop, and Coon: J. Biol. Chem. 259, 6812-6817 (1984)], excess NADPH and oxygen are consumed suggesting that a 4-electron reduction of oxygen to water occurs. Similar effects are seen with testosterone as substrate for the constitutive forms of P-450, RLM2 and RLM5. However, when aminopyrine or p-nitroanisole serve as substrate, none of the forms of P-450 consumed excess NADPH or oxygen. Thus, consumption of excess NADPH and oxygen appears to be the result of the substrate used. Cytochrome b5 stimulates turnover of LM2 and RLM5 but not RLM2. With LM2, it causes a metabolic switching to occur between the monooxygenase and the NADPH-oxidase reaction. Although RLM5 is also stimulated by cytochrome b5, no metabolic switching occurs. Cytochrome b5 did not affect the proportion of excess NADPH or oxygen consumed.

Animals↗
PubMed1983

[Effect of cytochrome b5 on the functional activity and conformational state of cytochrome P-450].

Microsomal cytochromes P-450 and b5 were shown to form mixed complexes with the association constant of 0.24 microM in water solution. Such complex formation stabilizes cytochrome P-450 in the catalytically active conformational state characterized by increased conformational rigidity and temperature stability. This stabilization results in acceleration of the cumene hydroperoxide-dependent oxidation of p-nitroanisol catalyzed by cytochrome P-450. The thermodynamic parameters of O-demethylation of p-nitroanisol catalyzed by cytochrome P-450 and mixed haemoprotein complexes measured in water solution and in a membrane-bound state were found to be different.

Cytochrome P-450 Enzyme System↗
PubMed1993

Interaction of non-myristoylated NADH-cytochrome b5 reductase with cytochrome b5-dimyristoylphosphatidylcholine vesicles.

An expression vector for NADH-cytochrome b5 reductase containing a thrombin cleavage site directly before the N-terminal glycine residue of the flavoprotein was used to isolate the non-myristoylated enzyme by thrombin cleavage of the initial fusion protein of a short segment of the multiple cloning site of the plasmid vector and the reductase. This flavoprotein preparation, containing only the 28-residue N-terminal peptide segment of the membrane-binding domain of the mammalian enzyme, binds to phospholipid vesicles and interacts with membrane-bound cytochrome b5. The effect of N-myristoylation of the enzyme therefore appears to be limited to facilitating and stabilizing interactions with phospholipid vesicles. However, the relatively short intervening peptide sequence that separates the crucial peptide membrane-binding domain from lysine 41, which has been implicated in the active-site interaction with cytochrome b5 (Strittmatter, P., Kittler, J. M., Coghill, J. E., and Ozols, J. (1992) J. Biol. Chem. 267, 2519-2523), provides some limitation of the distance from the membrane surface for the interactions required for rapid electron transfer from the flavin of the reductase to the heme of cytochrome b5.

Base Sequence↗
PubMed1987

Nuclear functions required for cytochrome c oxidase biogenesis in Saccharomyces cerevisiae: multiple trans-acting nuclear genes exert specific effects on expression of each of the cytochrome c oxidase subunits encoded on mitochondrial DNA.

Fourteen nuclear complementation groups of mutants that specifically affect the three mitochondrially-encoded subunits of yeast cytochrome c oxidase have been characterized. Genes represented by these complementation groups are not required for mitochondrial transcription, transcript processing, or translation per se but are required for the expression of one of the three genes--COX1, COX2, or COX3--which encode the cytochrome c oxicase subunits I, II, or III, respectively. Five of these genes affect the biogenesis of cytochrome c oxidase subunit I, 3 affect the biogenesis of subunit II, 3 affect the biogenesis of subunit III and 3 affect the biogenesis of both cytochrome c oxidase subunit I and cytochrome b, the product of COB. Among the 5 complementation groups of mutants that affect the expression of COX1, 2 lack COX1 transcripts, 1 produces incompletely processed COX1 transcripts, and 2 contain normal levels of normal-sized COX1 transcripts. In contrast, all 3 complementation groups which affect the expression of COX2 and all 3 complementation groups which affect the expression of COX3 exhibit no, or little, detectable difference with respect to the wild type pattern of transcripts. The 3 complementation groups which affect the expression of both COX1 and COB all have aberrant COX1 and COB transcript patterns. These findings indicate that multiple trans-acting nuclear genes are required for specific expression of each COX gene encoded on mitochondrial DNA and suggest that their products act at different steps in the expression of these mitochondrial genes.

Cell Nucleus↗
PubMed1978

Studies on the orientations of the mitochondrial redox carriers. I. Orientation of the hemes of cytochrome c oxidase with respect to the plane of a cytochrome oxidase-lipid model membrane.

The liganded derivatives of mitochondrial cytochrome c oxidase have been prepared in hydrated oriented multilayers of membranous cytochrome c oxidase. The optical spectra of the liganded derivatives recorded at an angle of 45 degrees between the incident light beam and the normal to the planes of the membranes in the multilayers show dichroic ratios of almost 2 in the visible region and 1.2-1.4 in the Soret region. The dichroic ratios were found to be similar for both cytochromes a and a3. Electron paramagnetic resonance spectra of the azide, sulfide, and formate complexes of cytochrome c oxidase obtained as a function of the orientation of the applied magnetic field relative to the planes of the membranes in the multilayer confirm the optical data and demonstrate that both hemes of cytochrome c oxidase are oriented such that the angle between the heme normal and the membrane normal is approximately 90 degrees.

Animals↗
PubMed1992

The formate complex of the cytochrome bo quinol oxidase of Escherichia coli exhibits a 'g = 12' EPR feature analogous to that of 'slow' cytochrome oxidase.

The cytochrome bo quinol oxidase of Escherichia coli is homologous in sequence and in structure to cytochrome aa3 type cytochrome oxidase in subunit I, which contains the catalytic core. The cytochrome bo enzyme forms a formate complex which exhibits 'g = 12' and 'g = 2.9' EPR signals at X band; similar signals have previously been observed only in association with the 'slow' and formate-ligand states of cytochrome oxidase. These signals arise from transitions within integral spin multiples identified with the homologous heme-copper binuclear catalytic centers in both enzymes.

Bacterial Proteins↗