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PubMed1985

Electron-paramagnetic-resonance studies of structure and function of the two-haem enzymes Pseudomonas cytochrome c peroxidase and beef heart cytochrome c oxidase.

Beef heart cytochrome c oxidase contains two cytochromes, a and a3, and Pseudomonas aeruginosa cytochrome c peroxidase has one high- and one low-potential c haem, cHP and cLP. The parallelism in co-ordination and spin states between cytochrome a and haem cHP on the one hand and between cytochrome a3 and haem cLP on the other is illustrated. The two latter haems become accessible to cyanide, when the former are reduced. Such reduction also leads to an activation of the enzymes. Mechanisms are presented in which ferryl forms of cytochromes a3 and haem cLP take part. The enzymes reach an oxidation state, formally the same as resting enzyme, but with different properties.

Animals↗
PubMed2003

Induction of SM-20 in PC12 cells leads to increased cytochrome c levels, accumulation of cytochrome c in the cytosol, and caspase-dependent cell death.

Sympathetic neurons deprived of nerve growth factor (NGF) release cytochrome c into the cytosol and undergo caspase-dependent cell death through a process that requires de novo gene expression. Expression of the SM-20 gene increases after NGF withdrawal, and ectopic SM-20 expression induces cell death in NGF-maintained neurons. To further evaluate the mechanism by which SM-20 promotes cell death, we developed a PC12-derived cell line in which SM-20 expression can be induced by addition of doxycycline to the culture medium. Induction of SM-20 in either undifferentiated or NGF-differentiated cells resulted in cell death. Cell death was accompanied by an increase in caspase activity and was inhibited by the caspase inhibitor zVAD-FMK. Analysis of cytochrome c in cytosolic and mitochondria-enriched subcellular fractions revealed that induction of SM-20 led to the accumulation of cytochrome c in the cytosol. Surprisingly, SM-20 expression also resulted in a selective increase in the total amount of cytochrome c protein. Thus, induction of SM-20 expression appears to affect both the amount and subcellular localization of cytochrome c in PC12 cells. These results suggest that SM-20 promotes caspase-dependent cell death through a mechanism involving cytochrome c.

Animals↗
PubMed1972

Aerobic reduction of cytochrome b 566 in pigeon-heart mitochondria (succinate-cytochrome C1 reductase-stopped-flow kinetics).

In anaerobic, uncoupled pigeon-heart mitochondria treated with oxidizable substrate, the cytochrome b(566) remains largely oxidized. In the presence of antimycin A, addition of oxygen induces a reduction of this cytochrome. The rate of cytochrome b(566) reduction is comparable to and dependent on the rate of cytochrome c(1) oxidation. Kinetic data suggest that either ubiquinone or another donor of similar potential provides electrons for the reduction of cytochrome b(566). It is postulated that the aerobic reduction of cytochrome b(566) is directly related to the energy conservation at site II.

Aerobiosis↗
PubMed1977

Structure of cytochrome c555 of Chlorobium thiosulfatophilum: primitive low-potential cytochrome c.

Cytochrome c555 is an 86-residue type c cytochrome derived from Chlorobium thiosulfatophilum, an obligately anaerobic green sulfur bacterium which is among the most primitive of living organisms. Here is presented a preliminary structural description of the cytochrome c555 molecule based on its crystallographic structure determination at 2.7-A resolution by multiple isomorphous replacement methods. This structure is of interest not only because of its evolutionary significance but also because the cytochrome c555 molecule possesses an unusually low physiologic oxidoreduction potential (Em,7 = +145 mV) compared with related members of the cytochrome c family. Consequently, determination of its structure may permit a direct assessment of the structural factors responsible for prosthetic group redox potential regulation in type c cytochromes.

Bacteria↗
PubMed1984

Structures of cysteine-containing peptides in isosafrole-inducible rat hepatic microsomal cytochrome P-450d: sequence homology with 3-methylcholanthrene-induced cytochrome P-450c.

Six cysteine-containing tryptic peptides were isolated from rat liver cytochrome P-450d, the major isosafrole-induced isozyme, by reversed-phase high performance liquid chromatography. The six peptides contained a total of seven cysteine residues. Five of the peptides have significant sequence homology (20/22, 10/16, 8/13, 13/18, and 5/9 identical residues) to cysteine-containing peptides in cytochrome P-450c, the major isozyme induced by 3-methylcholanthrene. One of the peptides (partial sequence, Cys-Ile-Gly-Glu-Ile-Pro-Ala-Lys-Trp-Glu-Val-Phe-Leu-) can be included in the highly conserved COOH-terminal domain found in all cytochromes P-450 that have been sequenced. Although this domain has been postulated as the heme-binding domain by some investigators, it is not homologous to the heme-binding region in cytochrome P-450cam. A second peptide (partial sequence, Asp-Pro-Thr-Ser-Val-Ser-Ser-Cys-Tyr-Leu-Glu-Glu-His-Val-Ser-Lys) is, however, a possible candidate for the heme attachment site to cysteine because of its weak homology to the heme-binding site in cytochrome P-450cam. These results indicate that either the location of the heme-binding site is different in various forms of cytochromes P-450 or the amino acid sequence surrounding the heme-binding cysteine is not highly conserved among these proteins.

Amino Acid Sequence↗
PubMed1995

Degradation of cytochrome oxidase subunits in mutants of yeast lacking cytochrome c and suppression of the degradation by mutation of yme1.

We have confirmed by spectral analysis that cytochrome oxidase is not present in strains of the yeast Saccharomyces cerevisiae having a primary deficiency in cytochrome c, and we have demonstrated by immunological procedures that such strains lack the mitochondrially encoded subunits I, II, and III of cytochrome oxidase. Furthermore, pulse-chase experiments demonstrated that subunit II is rapidly degraded in vivo. This degradation can be at least partially suppressed by disruption of the nuclear gene YME1, which encodes a putative ATP-Zn(2+)-dependent protease. We suggest that the cytochrome oxidase subunits are not properly assembled in the absence of cytochrome c, and that Yme1 and possibly other proteases degrade the unassembled mitochondrial-encoded subunits of cytochrome oxidase.

ATP-Dependent Proteases↗
PubMed1995

Design of a ruthenium-cytochrome c derivative to measure electron transfer to the initial acceptor in cytochrome c oxidase.

A ruthenium-labeled cytochrome c derivative was prepared to meet two design criteria: the ruthenium group must transfer an electron rapidly to the heme group, but not alter the interaction with cytochrome c oxidase. Site-directed mutagenesis was used to replace His39 on the backside of yeast C102T iso-1-cytochrome c with a cysteine residue, and the single sulfhydryl group was labeled with (4-bromomethyl-4' methylbipyridine) (bis-bipyridine)ruthenium(II) to form Ru-39-cytochrome c (cyt c). There is an efficient pathway for electron transfer from the ruthenium group to the heme group of Ru-39-cyt c comprising 13 covalent bonds and one hydrogen bond. Electron transfer from the excited state Ru(II*) to ferric heme c occurred with a rate constant of (6.0 +/- 2.0) x 10(5) s-1, followed by electron transfer from ferrous heme c to Ru(III) with a rate constant of (1.0 +/- 0.2) x 10(6) s-1. Laser excitation of a complex between Ru-39-cyt c and beef cytochrome c oxidase in low ionic strength buffer (5 mM phosphate, pH7) resulted in electron transfer from photoreduced heme c to CuA with a rate constant of (6 +/- 2) x 10(4) s-1, followed by electron transfer from CuA to heme a with a rate constant of (1.8 +/- 0.3) x 10(4) s-1. Increasing the ionic strength to 100 mM leads to bimolecular kinetics as the complex is dissociated. The second-order rate constant is (2.5 +/- 0.4) x 10(7) M-1s-1 at 230 mM ionic strength, nearly the same as that of wild-type iso-1-cytochrome c.

Animals↗
PubMed1999

Definition of the interaction domain for cytochrome c on cytochrome c oxidase. III. Prediction of the docked complex by a complete, systematic search.

The electron transfer complex between bovine cytochrome c oxidase and horse cytochrome c has been predicted with the docking program DOT, which performs a complete, systematic search over all six rotational and translational degrees of freedom. Energies for over 36 billion configurations were calculated, providing a free-energy landscape showing guidance of positively charged cytochrome c to the negative region on the cytochrome c oxidase surface formed by subunit II. In a representative configuration, the solvent-exposed cytochrome c heme edge is within 4 A of the indole ring of subunit II residue Trp(104), indicating a likely electron transfer path. These two groups are surrounded by a small, hydrophobic contact region, which is surrounded by electrostatically complementary hydrophilic interactions. Cytochrome c/cytochrome c oxidase interactions of Lys(13) with Asp(119) and Lys(72) with Gln(103) and Asp(158) are the most critical polar interactions due to their proximity to the hydrophobic region and exclusion from bulk solvent. The predicted complex matches previous mutagenesis, binding, and time-resolved kinetics studies that implicate Trp(104) in electron transfer and show the importance of specific charged residues to protein affinity. Electrostatic forces not only enhance long range protein/protein association; they also predominate in short range alignment, creating the transient interaction needed for rapid turnover.

Animals↗
PubMed1976

Isolation and partial charcterization of a cytochrome b complex and cytochrome oxidase from yeast mitochondria.

A cytochrome b complex and cytochrome oxidase have been purified 14- and 20-fold respectively from yeast submitochondrial particles by a simple procedure involving their spontaneous precipitation from a deoxycholate extract. The recovery of both proteins was almost quantitative. The specific heme contents were 11 and 8 nmoles/mg protein for the cytochrome b complex and cytochrome oxidase respectively and both were spectrally pure. Sodium dodecyl sulfate gel electrophoresis resolved the cytochrome b complex into seven distinct subunits with molecular weights 42,000, 33,000, 27,500, 23,000, 15,500, 13,000 and 10,500. Cytochrome oxidase contained five bands with molecular weights 42,000, 26,500, 21,000, 14,000 and 10,500.

Cytochromes↗
PubMed2004

Development of microarray-based diagnostics of voles and shrews for use in biodiversity monitoring studies, and evaluation of mitochondrial cytochrome oxidase I vs. cytochrome b as genetic markers.

Molecular methods are widely used for species identification of mammals. In particular, the mitochondrial cytochrome b gene sequence has proven helpful for this purpose. Microarray technology can now open up new perspectives for biodiversity monitoring. With microarrays, many thousands of genetically based characteristics can be tested on one microscopic glass slide called a 'chip'. A 'Mammalia-Chip', for example, could include redundant diagnostic markers to unambiguously identify all European mammal species. Of broader use, and therefore economically more relevant, could be a 'Biodiversity-Chip', containing diagnostic features to distinguish key species in the taxa of bacteria, lichen, molluscs, insects, fungi, mammals, etc. An important prerequisite for any mixed-phyla chip is a standardization of methods. One of the most promising genes as a universal marker for all eukaryotes is cytochrome oxidase I. We show that cytochrome oxidase I is adequate for the discrimination of different species of voles and shrews with cluster analysis. Based on these results we present a diagnostic microarray-chip using cytochrome oxidase I sequences for the identification of three species of Sorex (Soricidae, Insectivora) and four species of Microtus (Arvicolinae, Rodentia). We conclude that cytochrome oxidase I can be used as an alternative marker to cytochrome b in a mixed-phyla chip, or both genes can be used in combination to enhance redundance and thus robustness of a specific chip including small mammals.

Animals↗
PubMed1996

Alteration of haem-attachment and signal-cleavage sites for Paracoccus denitrificans cytochrome C550 probes pathway of c-type cytochrome biogenesis in Escherichia coli.

Paracoccus denitrificans cytochrome C550 is expressed as a periplasmic holo-protein in Escherichia coli; amino acid substitutions of cysteine residues in the haem-binding motif (Cys-X-X-Cys-His), either together or singly, prevented covalent attachment of haem but not polypeptide translocation into the periplasm. When the three alanine residues at positions -3 to -1 in the native signal-cleavage site were deleted, or alanine at -1 was changed to glutamine, signal cleavage was at alternative sites (after only ten residues in the latter case), but haem attachment still occurred. When the same three alanines were changed to Asp-Glu-Asp, a membrane-associated apo product that had retained the complete signal sequence was detected. These and other results presented here indicate that (i) haem attachment is not required for the apo-cytochrome C550 export to the periplasm; (ii) haem cannot attach to apo-cytochrome C550 when attached to the cytoplasmic membrane, suggesting that signal-sequence cleavage precedes periplasmic haem attachment, which can occur at as few as six residues from the mature N-terminus; and (iii) two cysteines are required for haem attachment, possibly because a disulphide bond is an intermediate. The gene for Saccharomyces cerevisiae mitochondrial iso-1-cytochrome c was expressed as a holo-protein in E. coli when fused with the signal sequence plus the first 10 residues of the mature cytochrome C550, indicating that the E. coli cellular apparatus for the c-type cytochrome biogenesis has a broad substrate specificity.

Amino Acid Sequence↗
PubMed1983

Is cytochrome b really the antimycin-binding component of the cytochrome b--c1 complex of yeast mitochondria.

1. The antimycin binding sites were found to be independent of cytochrome(s) b synthesis in pseudo-wild-type revertants of cytochrome b mutants. These revertants, whose primary mutation is located in the introns of the cob-box gene of mitochondrial DNA, have modified contents of cytochromes b-562 and b-565 and fully functional respiratory chain. 2. Missense mutations in three genetic loci allocated to the exons of the cytochrome b gene, abolish the strong affinity binding of antimycin. 3. It is proposed that the antimycin-binding component is not cytochrome b itself, but interacts with it in such a way that an alteration of the cytochrome b structure affects the antimycin-binding site.

Antimycin A↗
PubMed1993

Rapid screening of cytochromes of respiratory mutants of Saccharomyces cerevisiae. Application to the selection of strains containing novel forms of cytochrome-c oxidase.

A technique has been developed for the direct analysis by visible spectrophotometry of yeast spots growing on agar plates. This allows rapid semi-quantitative estimations of cytochromes c, b and oxidase and permits the identification of strains with impaired respiratory electron flow. Results of screening of 105 mutants are presented. There appears to be a correlation between the exonic location of the mutation in COX1 of oxidase and the level of optically detectable enzyme. Mutations in cytochrome b of the bc1 complex also affect the level of expression of cytochrome oxidase and can cause either an increased or decreased level of expression of oxidase relative to the wild-type strain. Twelve strains selected by the rapid level-1 screening were grown as lawns on sections of an agar plate and resuspended for a second level of screening. Quantitative estimates have been made of the concentrations of cytochromes, the turnover number of cytochrome oxidase and the kinetics of recombination of carbon monoxide with oxidase after flash photolysis. This confirmed the validity of the rapid screening procedure, and we have identified several strains which contain high levels of a mutant form of cytochrome oxidase with properties worthy of further investigation.

Cytochromes↗
PubMed1995

Immunoelectron microscopy and epitope mapping with monoclonal antibodies suggest the existence of an additional N-terminal transmembrane helix in the cytochrome b subunit of bacterial ubiquinol:cytochrome-c oxidoreductases.

The topology of the ubiquinol:cytochrome-c oxidoreductase (cytochrome bc1 complex) from Paracoccus denitrificans was investigated by immunoelectron microscopy with sequence-specific murine monoclonal antibodies. Epitope mapping with synthetic peptides and enzymic proteolytic cleavage of the cytochrome bc1 complex were employed to localize precisely the respective antibody epitopes on the subunits of this membrane protein complex. Localization of defined epitopes on the cytochrome bc1 complex by immunoelectron microscopy clearly demonstrates that the N-terminus of the cytochrome b subunit is exposed to the periplasmic space. This finding is in agreement with a nine-transmembrane-helices topology model (I-IX) as predicted before for cytochrome b. However, due to other published evidence we favour the existence of an additional transmembrane helix (helix 0) complementing a more recently published eight-helices model (A-C,cd, D-H), at least for prokaryotes.

Amino Acid Sequence↗
PubMed2005

OmcF, a putative c-Type monoheme outer membrane cytochrome required for the expression of other outer membrane cytochromes in Geobacter sulfurreducens.

Outer membrane cytochromes are often proposed as likely agents for electron transfer to extracellular electron acceptors, such as Fe(III). The omcF gene in the dissimilatory Fe(III)-reducing microorganism Geobacter sulfurreducens is predicted to code for a small outer membrane monoheme c-type cytochrome. An OmcF-deficient strain was constructed, and its ability to reduce and grow on Fe(III) citrate was found to be impaired. Following a prolonged lag phase (150 h), the OmcF-deficient strain developed the ability to grow in Fe(III) citrate medium with doubling times and yields that were ca. 145% and 70% of those of the wild type, respectively. Comparison of the c-type cytochrome contents of outer membrane-enriched fractions prepared from wild-type and OmcF-deficient cultures confirmed the outer membrane association of OmcF and revealed multiple changes in the cytochrome content of the OmcF-deficient strain. These changes included loss of expression of two previously characterized outer membrane cytochromes, OmcB and OmcC, and overexpression of a third previously characterized outer membrane cytochrome, OmcS, during growth on Fe(III) citrate. The omcB and omcC transcripts could not be detected in the OmcF-deficient mutant by either reverse transcriptase PCR or Northern blot analyses. Expression of the omcF gene in trans restored both the capacity of the OmcF-deficient mutant to reduce Fe(III) and wild-type levels of omcB and omcC mRNA and protein. Thus, elimination of OmcF may impair Fe(III) reduction by influencing expression of OmcB, which has previously been demonstrated to play a critical role in Fe(III) reduction.

Amino Acid Sequence↗
PubMed1990

Human neutrophil cytochrome b light chain (p22-phox). Gene structure, chromosomal location, and mutations in cytochrome-negative autosomal recessive chronic granulomatous disease.

A membrane-bound cytochrome b, a heterodimer formed by a 91-kD glycoprotein (heavy chain) and a 22-kD polypeptide (light chain), is an essential component of the phagocyte NADPH-oxidase responsible for superoxide generation. Cytochrome b is absent in two subgroups of chronic granulomatous disease (CGD), an inherited disorder characterized by the lack of oxidase activity. Mutations in the cytochrome heavy chain gene, encoded by the CYBB locus in Xp21.1, result in the X-linked form of CGD. A rare subgroup of autosomal recessive CGD also lacks cytochrome b (A- CGD), but the genetic defect has not previously been identified. In order to search for possible mutations in the cytochrome light chain locus, CYBA, the structure of this gene was characterized. The CYBA locus was localized to 16q24, and the approximately 600-bp open reading frame determined to be encoded by six exons that span approximately 8.5 kb. Three unrelated patients with A- CGD were studied for evidence of mutations in the light chain gene. One patient, whose parents were first cousins, was homozygous for a large deletion that removed all but the extreme 5' coding sequence of the gene. The other two patients had a grossly normal light chain transcript on Northern blot of mononuclear cell RNA. The light chain transcript was amplified by the polymerase chain reaction and sequenced. One patient was a compound heterozygote for two alleles containing point mutations in the open reading frame that predict a frame shift and a nonconservative amino acid replacement, respectively. The second patient, whose parents were second cousins, was homozygous for a different single-base substitution resulting in another nonconservative amino acid change. These results indicate that A- CGD can results from defects in the gene encoding the 22-kD light chain of the phagocyte cytochrome b.

Amino Acid Sequence↗
PubMed1990

Isoforms of mammalian cytochrome c oxidase: correlation with human cytochrome c oxidase deficiency.

We have reviewed the structure, function, and biogenesis of mammalian cytochrome c oxidase, examined the tissue-specific expression of isoforms of cytochrome c oxidase subunits in different mammals, and attempted to correlate the data with our knowledge of cytochrome c oxidase deficiency, illustrated by one particular patient. Cytochrome c oxidase was isolated from bovine tissues, and individual subunits examined by SDS-PAGE, N-terminal peptide sequencing, and antibody binding. Isoforms of subunits VIa, VIIa, and VIII were identified, manifesting one pattern of expression in heart and skeletal muscle, and another in liver, kidney, and brain. In rat heart and liver, only one form of subunit VIIa was identified. Northern analysis of bovine and rat tissues suggested that the tissue-specific expression of subunits VIa and VIII is regulated transcriptionally in liver, kidney, and brain, and posttranscriptionally in heart and skeletal muscle. In humans, antibody binding documented isoforms of subunits VIa and VIIa, with the pattern of expression in heart and skeletal muscle differing from that in liver, kidney, and brain; our data suggested that both isoforms of subunit VIa may be expressed in human heart. In a patient with cytochrome c oxidase deficiency, the clinical, morphologic, and biochemical manifestations were much more severe in heart than in skeletal muscle. Antibody binding suggested partial assembly of the enzyme in heart. These and other data suggest considerably more variability in the tissue-specific expression of isoforms of cytochrome c oxidase subunits than previously recognized.

Amino Acid Sequence↗
PubMed1983

Effect of environmental temperature on the content of cytochrome P-450 and activity of NADPH-cytochrome C reductase in rats.

The effect of environmental temperature on the content of cytochrome P-450 or the activity of nicotinamide adenine dinucleotide phosphate-cytochrome c (NADPH-cytochrome c) reductase was examined by using microsomes prepared from rats kept at 30 degrees C or 15 degrees C for 14 d. The warm exposure (30 degrees C for 14 d) resulted in a significant reduction of the activity of NADPH-cytochrome c reductase though the content of cytochrome P-450 was not changed. The level of thyroxine and 3,3',5-triiodothyronine was reduced by the warm exposure. From the present observation, it was suggested that the effect of environmental temperature on the metabolism of drugs was due to the activity of NADPH-cytochrome c reductase mediated by the level of thyroid hormone.

Animals↗