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PubMed1976

Change in the ratio of cytochrome oxidase activity to nitrite reductase activity of Pseudomonas aeruginosa nitrite reductase with the kind of C-type cytochrome used as an electron donor.

The ratio between the nitrite reductase and cytochrome oxidase activities of Pseudomonas aeruginosa nitrite reductase [EC 1.9.3.2.] varies with kind of C-type cytochrome used as the electron donor. Withe cytochrome c-548, 554 (Micrococcus sp.), the nitrite reductase activity is greater than the cytochrome oxidase activity, while the former is smaller than the latter with cytochrome c-554 (Navicula pelliculosa). The aerobic oxidation catalyzed by this enzyme of denitrifying bacterial ferrocytochrome c is greatly accelerated on addition of nitrite, while that of the algal ferrocytochrome c is not affected or is even depressed by the salt. An accelerative effect of nitrite is generally observed with many kinds of C-type cytochromes which react with the enzyme very or fairly rapidly. The difference in the ratio of the two activities of the enzyme seems to arise according to whether or not nitrite affects the interaction of C-type cytochrome with the enzyme.

Cytochrome c Group↗
PubMed1978

Nature of tryptic attack on cytochrome b5 and further evidence for the two-domain structure of the cytochrome molecule.

Rabbit cytochrome b5 was incorporated into single-walled phosphatidylcholine liposomes, and the cytochrome b5-liposome complex thus formed was digested with trypsin. Protein chemical characterization indicated that the main products formed were 1) a hydrophilic (heme-containing) fragment of the cytochrome corresponding to the sequence consisting of the masked NH2-terminus through residue 88, 2) a hydrophobic peptide which spans residue 91 to the COOH-terminus (residue 133), and 3) a dipeptide, seryl-lysine, derived from residues 89 and 90. The hydrophobic peptide was obtained in the form of its complex with liposomes. It was concluded that trypsin cleaved rather specifically the peptide bonds between residues 88 and 89 (Arg-Ser) and between residues 90 and 91 (Lys-Leu). Tryptic digestion of free, unbound cytochrome b5 also resulted in the cleavage of the same peptide bonds. These results are not consistent with the proposal of Visser et al. (Visser, L., Robinson, N.C., & Tanford, C. (1975) Biochemistry 14, 1194-1199) that the hydrophilic and hydrophobic domains of cytochrome b5 are connected to each other by a link peptide consisting of some 15 amino acid residues and that this link peptide can be cut out by the action of trypsin. The circular dichroism spectrum of intact cytochrome b5 or its complex with liposomes in the far-ultraviolet region was closely similar to the sum of the spectra of the hydrophilic fragment and the hydrophobic peptide (or its complex with liposomes). This indicates that the tryptic cleavage of the cytochrome molecule does not induce any significant changes in the conformations of the hydrophilic and hydrophobic moieties of the molecule and thus provides further evidence that the three-dimensional structures of the two domains are independent of each other.

Amino Acids↗
PubMed1982

Membrane-bound cytochromes c of Pseudomonas aeruginosa grown aerobically. Purification and characterization of cytochromes c-551 and c-555.

Membrane-bound cytochromes c of Pseudomonas aeruginosa grown aerobically were investigated. By detecting polypeptides with heme-catalyzing peroxidase activity on a sodium dodecyl sulfate polyacrylamide gel, four major (Band I, 33,000 daltons; II, 25,000; III, 20,000; IV, 16,000) and one minor (V, 11,500) hemoproteins were found in the membrane fraction, while one hemoprotein (VI, 8,200) was detected in a small amount in the cytosol fraction. All these hemoproteins (bands I to VI) appeared to be cytochromes c, because all bands were detected even after being treated with HCl-acetone. Of the membrane-bound cytochromes c, cytochromes c-551 (band IV) and c-555 (band V) were solubilized with Triton X-100 and purified by repeated DEAE-cellulose column chromatography. Both purified cytochromes c-551 and c-555 were monomeric and their molecular weights were estimated to be 16,400 and 11,500, respectively. Their respective midpoint potentials were 0.31 and 0.34 V, and their respective isoelectric points in the reduced form were 3.8 and 5.2. The purified cytochromes c-551 and c-555 were found to be clearly different from "soluble" cytochrome c-551, and might function in the membrane-bound aerobic respiratory chain of P. aeruginosa.

Amino Acids↗
PubMed1984

Multiple forms of hepatic cytochrome P-450. Purification, characterisation and comparison of a novel clofibrate-induced isozyme with other major forms of cytochrome P-450.

In the present studies, a novel form of highly purified cytochrome P-450 (cytochrome P-452) isolated from the hepatic microsomes of clofibrate-pretreated rats has been compared to the major isozymes isolated from the hepatic microsomes of rats pretreated with phenobarbital (cytochrome P-450) and 2-naphthoflavone (cytochrome P-447) using a number of biochemical criteria. The results show that these three isozymes exhibit marked structural differences from each other as judged by a complete lack of immunochemical cross-reactivity between the isozymes and the heterologous rabbit serum antibodies using Ouchterlony double diffusion, and non-identity between the limited proteolytic digestion maps of the three isozymes obtained in the presence of chymotrypsin, papain and Staphylococcus aureus V8 proteases. Furthermore, the three isozymes exhibited clear differences in their monomeric molecular weights determined on calibrated sodium dodecyl sulphate/polyacrylamide gel electrophoresis in gels of varying acrylamide concentration. Substantial differences were also observed in the substrate specificities of the isozymes, which were reflected in differences in the turnover rates and positional selectivities of the hemoproteins for some model substrates. In addition, the isozymes differed in their substrate binding affinities and their ability to interact with purified hepatic microsomal cytochrome b5, as judged using difference spectrophotometry. Finally, subtle differences were detected in the ultraviolet visible absorbance spectra of the hemoproteins in the ferric, ferrous, and carbonmonoxyferrous states. Taken collectively, the above data provides compelling evidence that fundamental differences exist between these cytochrome P-450 isozymes, further establishing the uniqueness of the major form of cytochrome P-450 induced by clofibrate pretreatment.

Animals↗
PubMed1987

Import of cytochrome c into mitochondria. Cytochrome c heme lyase.

The import of cytochrome c into mitochondria can be resolved into a number of discrete steps. Here we report on the covalent attachment of heme to apocytochrome c by the enzyme cytochrome c heme lyase in mitochondria from Neurospora crassa. A new method was developed to measure directly the linkage of heme to apocytochrome c. This method is independent of conformational changes in the protein accompanying heme attachment. Tryptic peptides of [35S]cysteine-labelled apocytochrome c, and of enzymatically formed holocytochrome c, were resolved by reverse-phase HPLC. The cysteine-containing peptide to which heme was attached eluted later than the corresponding peptide from apocytochrome c and could be quantified by counting 35S radioactivity as a measure of holocytochrome c formation. Using this procedure, the covalent attachment of heme to apocytochrome c, which is dependent on the enzyme cytochrome c heme lyase, could be measured. Activity required heme (as hemin) and could be reversibly inhibited by the analogue deuterohemin. Holocytochrome c formation was stimulated 5--10-fold by NADH greater than NADPH greater than glutathione and was independent of a potential across the inner mitochondrial membrane. NADH was not required for the binding of apocytochrome c to mitochondria and was not involved in the reduction of the cysteine thiols prior to heme attachment. Holocytochrome c formation was also dependent on a cytosolic factor that was necessary for the heme attaching step of cytochrome c import. The factor was a heat-stable, protease-insensitive, low-molecular-mass component of unknown function. Cytochrome c heme lyase appeared to be a soluble protein located in the mitochondrial intermembrane space and was distinct from the previously identified apocytochrome c binding protein having a similar location. A model is presented in which the covalent attachment of heme by cytochrome c heme lyase also plays an essential role in the import pathway of cytochrome c.

Chromatography, High Pressure Liquid↗
PubMed1992

Point mutation in cytochrome b of yeast ubihydroquinone:cytochrome-c oxidoreductase causing myxothiazol resistance and facilitated dissociation of the iron-sulfur subunit.

Cytochrome-c reductase was isolated from Saccharomyces cerevisiae GM50-3C. A tenth subunit was detected with molecular mass 8.5 kDa on SDS/PAGE. Two yeast mutants selected for resistance to myxothiazol, an inhibitor of the Q0 center (Q, ubiquinone) of cytochrome-c reductase, were analysed. The single amino acid substitution in the cytochrome-b subunit, N256Y in the mutant Myx-119 and G137R in the mutant Myx-118, caused a general resistance to all methoxyacrylate inhibitors to about fivefold higher concentrations. The kinetic measurements with the substrate analogue nonylbenzohydroquinone revealed a decrease in the Km by fivefold and of the maximal turnover number by fourfold in the N256Y mutant. The Km of the G137R mutant was not affected and the Vmax was 50% higher. Cytochrome-c reductase was isolated from mutants to allow determination of the Kd values of methoxyacrylate-stilbene and myxothiazol by means of fluorescence-quench and red-shift titration. Changes in the structure of the multisubunit complex due to a single amino acid exchange became obvious during the purification procedure. SDS/PAGE of the purified enzyme revealed that the substitution N256Y in cytochrome b led to a loss of the iron-sulfur protein and the fifth small subunit with no change in the pattern of the remaining eight subunits. The subunit pattern of the G137R mutant was identical to the wild type. This is the first report of a single amino acid exchange in the catalytic subunit of cytochrome b, greatly affecting the iron-sulfur protein, the second important catalytic subunit of the Q0 center. This is a new approach to obtain structural information about the interaction of cytochrome b with the iron-sulfur subunit.

Amino Acid Sequence↗
PubMed2006

The expression of cytochrome P-450 and cytochrome P-450 reductase genes in the simultaneous transformation of corticosteroids and phenanthrene by Cunninghamella elegans.

The expression of cytochrome P-450 and cytochrome P-450 reductase (CPR) genes in the conterminous biotransformation of corticosteroids and PAHs was studied in Cunninghamella elegans 1785/21Gp. We had previously used this strain as a microbial eucaryotic model for studying the relationship between mammalian steroid hydroxylation and the metabolization of PAHs. We reported that cytochrome P-450 reductase is involved in the biotransformaton of cortexolone and phenanthrene. RT-PCR and Northern blotting analyses indicated that the cytochrome P-450 and CPR genes appear to be inducible by both steroids and PAHs. The expression of the cytochrome P-450 gene was increased ninefold and the expression of the CPR gene increased 6.4-fold in cultures with cortexolone and/or phenanthrene in comparison with controls. We conclude that the increase in cytochrome P-450 gene expression was accompanied by an increase in cytochrome P-450 enzymatic activity levels.

Biotransformation↗
PubMed2005

Cytochrome c maturation and the physiological role of c-type cytochromes in Vibrio cholerae.

Vibrio cholerae lives in different habitats, varying from aquatic ecosystems to the human intestinal tract. The organism has acquired a set of electron transport pathways for aerobic and anaerobic respiration that enable adaptation to the various environmental conditions. We have inactivated the V. cholerae ccmE gene, which is required for cytochrome c biogenesis. The resulting strain is deficient of all c-type cytochromes and allows us to characterize the physiological role of these proteins. Under aerobic conditions in rich medium, V. cholerae produces at least six c-type cytochromes, none of which is required for growth. Wild-type V. cholerae produces active fumarate reductase, trimethylamine N-oxide reductase, cbb3 oxidase, and nitrate reductase, of which only the fumarate reductase does not require maturation of c-type cytochromes. The reduction of nitrate in the medium resulted in the accumulation of nitrite, which is toxic for the cells. This suggests that V. cholerae is able to scavenge nitrate from the environment only in the presence of other nitrite-reducing organisms. The phenotypes of cytochrome c-deficient V. cholerae were used in a transposon mutagenesis screening to search for additional genes required for cytochrome c maturation. Over 55,000 mutants were analyzed for nitrate reductase and cbb3 oxidase activity. No transposon insertions other than those within the ccm genes for cytochrome c maturation and the dsbD gene, which encodes a disulphide bond reductase, were found. In addition, the role of a novel CcdA-like protein in cbb3 oxidase assembly is discussed.

Base Sequence↗
PubMed1995

Simulataneous isolation of NADPH-cytochrome P-450 reductase and cytochrome P-450 using tentacle ion-exchange chromatography and interspecies comparison of the reductase activity.

Using the same initial Fractogel (tentacle) ion-exchange chromatography to isolate murine cytochrome P-450, mouse hepatic NADPH-cytochrome P-450 reductase (EC 1.6.2.4) was simultaneously isolated from solubilized liver microsomes and purified on a DE-52 column to a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme had a molecular mass of 77 kD, and its specific activity was 25.4 mumol.min-1.mg protein-1. Purified constitutive mouse liver NADPH-cytochrome P-450 reductase was successfully reconstituted in vitro with dilauroylphosphatidyl-choline and constitutive purified mouse testosterone 2 alpha-hydroxylase (cytochrome P-450(2)alpha) with an observed activity of 13.8 nmol.min-1.nmol P-450-1. Although the partially purified reductase obtained from the Fractogel column was contaminated by significant levels of two unidentified proteins, it was as equally effective in the reconstituted system as the DE-52-derived purified reductase. Lastly, we found that rat and mouse NADPH-cytochrome P-450 reductases were similarly effective in supporting the catalytic activity of rat cytochrome P-450 2B1, but the murine reductase was 50% more effective than the rat reductase in a reconstituted system containing mouse cytochrome P-450(2)alpha.

Animals↗
PubMed2003

Distinct roles of endoplasmic reticulum cytochrome b5 and fused cytochrome b5-like domain for rat Delta6-desaturase activity.

The Delta6-desaturase catalyzes key steps in long-chain polyunsaturated fatty acid biosynthesis. Although the gene coding for this enzyme has been isolated in diverse animal species, the protein structure remains poorly characterized. In this work, rat Delta6-desaturase expressed in COS-7 cells was shown to localize in the endoplasmic reticulum. As the enzyme contains an N-terminal cytochrome b5-like domain, we investigated by site-directed mutagenesis the role of this domain in the enzyme activity. The typical HPGG motif of the cytochrome b5-like domain, and particularly histidine in this motif, is required for the activity of the enzyme, whatever the substrate. Neither endogenous COS-7 cytochrome b5 nor coexpressed rat endoplasmic reticulum cytochrome b5 could rescue the activity of mutated forms of Delta6-desaturase. Moreover, when rat endoplasmic reticulum cytochrome b5 was coexpressed with wild-type desaturase, both proteins interacted and Delta6-desaturase activity was significantly increased. The identified interaction between these proteins is not dependent on the desaturase HPGG motif. These data suggest distinct and essential roles for both the desaturase cytochrome b5-like domain and free endoplasmic reticulum cytochrome b5 for Delta6-desaturase activity.

Animals↗
PubMed1978

Interaction of cyanoketone and other steroid nitriles with cytochrome oxidase, hemoglobin, and cytochrome P-450.

The inhibitory activity of cyanoketone (CNK; 2alpha-cyano-4,4,17alpha-trimethyl-17beta-hydroxy-5-androsten-3-one), was investigated for enzymes of the respiratory chain and cholesterol side chain cleavage (CSCC). In bovine corpus luteum mitochondria incubated with [26-14C]cholesterol, 500 micron CNK caused 90% inhibition of pregnenolone synthesis. Comparable results were obtained with adrenal and placental mitochondria. Addition of CNK to bovine corpus luteum mitochondria or to cytochrome P-450 purified from this source elicited a concentration-dependent, reverse type I difference spectrum with an absorption maximum at about 423 nm and a minimum at about 395 nm, confirming binding to oxidized cytochrome P-450. This spectral change resembles those of steroids which inhibit CSCC. In mitochondrial preparations, CNK induced a second peak at about 445 nm. This peak was similar to that elicited by the interaction of potassium cyanide with cytochrome a3 when the former is added to rabbit heart mitochondria which are devoid of P-450. Like cyanide, CNK block mitochondrial respiration at the cytochrome oxidase site, and induced spectral changes in human hemoglobin. Therefore, this peak at 445 nm probably represents the interaction of CNK with oxidized cytochrome a3. Several other steroid nitriles had little, if any, effect on CSCC activity, nor did they induce spectral changes with cytochrome oxidase or hemoglobin. It appears that the steroid configuration of CNK is responsible for the binding to P-450 and inhibition of CSCC, whereas the binding to cytochrome a3 and hemoglobin and the inhibitory effect on electron transfer are probably related to the cyano group of CNK.

Androstenols↗
PubMed1980

Inhibition of the cytochrome c/cytochrome c oxidase system by cytochrome c derivatives and related fragments.

The oxidation of ferrocytochrome c mediated by cytochrome c oxidase was investigated in the presence of ferricytochrome c, trifluoroacetyl-cytochrome c, the heme fragments Hse65-[1-65] and Hse80-[1-80] and their respective porphyrin derivatives, as well as carboxymethylated apoprotein and related fragments, polycations, salts and neutral additives. The inhibition of the redox reaction by salts and neutral molecules, even if in theoretical agreement with their effect on electrostatic interactions, may alternatively be interpreted in terms of hydrophobicity. The latter can account for the inhibitory properties of trifluoroacetylated ferricytochrome c, similar to those of ferricytochrome c. On the assumption that the inhibitory properties of some of the investigated derivatives monitor their binding affinities to the cytochrome c oxidase at the cytochrome c binding sites, the experimental results do not confirm a primarily electrostatic character for the cytochrome c/cytochrome c oxidase association process. Strong indication was found that the cytochrome c C-terminal sequence is critically involved in the complex formation. Conformational studies by circular dichroism measurements and IR spectroscopy in solution and in solid state respectively, show that some of the derivatives examined may possibly acqkuire in the binding process to the oxidase, as secondary structure similar to that present in the native cytochrome c.

Amino Acids↗
PubMed1981

The effect of trifluoroacetyl-cytochrome c on the cytochrome c/cytochrome c oxidase reaction.

The importance of electrostatic interactions to the reaction between cytochrome c and cytochrome c oxidase is indicated most directly by the rapid increase in Km as ionic strength is increased. However, Chessa et al. (1980, Hoppe-Seyler's Z. Physiol. Chem. 361, 1077--1091) have recently found that a cytochrome c derivative trifluoroacetylated at all 19 lysine amino groups decreased the reaction rate between ferrocytochrome c and cytochrome c oxidase nearly as much as native ferricytochrome c, a known inhibitor that binds cytochrome c oxidase. They suggested that this was due to the formation of an inhibitory complex between trifluoroacetyl-cytochrome c and cytochrome c oxidase, which would argue against the importance of electrostatic interactions to the native complex. We have demonstrated that this apparent inhibition is in fact caused by a rapid electron transfer between native ferrocytochrome c and trifluoroacetyl-ferricytochrome c which decreases the concentration of native ferrocytochrome c, thus decreasing the reaction rate.

Animals↗
PubMed2001

Hsp27 inhibits cytochrome c-mediated caspase activation by sequestering both pro-caspase-3 and cytochrome c.

Mitochondrial cytochrome c release in response to pro-apoptotic signals leads to the formation of a cytochrome c/Apaf-1/procaspase-9 complex (the apoptosome) and resultant activation of caspase-9 and caspase-3. Here we demonstrate that the molecular chaperone, Hsp27, inhibits this cytochrome c-mediated activation of caspase-3. Immunodepeletion of Hsp27 from cytochrome c-activated cytosols resulted in decreased caspase activity. Furthermore, immunoprecipitation of Hsp27 resulted in the coprecipitation of both cytochrome c and procaspase-3. In reciprocal experiments, immunoprecipitation of both procaspase-3 and cytochrome c resulted in coprecipitation of Hsp27, indicating two independent interactions. These results point to Hsp27 mediating its inhibition of procaspase-3 activation through its ability to sequester both cytochrome c and procaspase-3, and thus prevent the correct formation/function of the apoptosome complex.

Apoptosis↗
PubMed1992

Cytochrome c reductase purified from Crithidia fasciculata contains an atypical cytochrome c1.

Cytochrome c reductase purified from the trypanosomatid Crithidia fasciculata retained antimycin A sensitivity and catalyzed the reduction of horse heart ferricytochrome c in the presence of reduced coenzyme Q10. The complex contained heme b and heme c1 in a ratio of 2:1. Nine major protein bands ranging in size from 55.3 to approximately 12.8 kDa were resolved by SDS-polyacrylamide gel electrophoresis. A 31.6-kDa protein was identified as cytochrome c1 by the presence of a covalently attached heme. A red shift in the alpha-absorbance band of the cytochrome c1 absolute absorbance spectrum, difference absorbance spectrum, and pyridine ferrohemochrome absorbance spectrum suggested that the heme prosthetic group of C. fasciculata cytochrome c1 is bound to the apoprotein through only one thioether bond. A fragment of the cytochrome c1 gene was amplified from C. fasciculata, Trypanosoma brucei, Leishmania tarentolae, and Bodo caudatus. The deduced heme binding site sequence of each of these kinetoplastid species, Phe-Ala-Pro-Cys-His, contains a phenylalanine rather that a cysteine at the first position so that only one thioether bond can be formed between heme and apoprotein. This phenylalanine substitution and the presence of a conserved proline in the sequence may represent compensatory changes that are necessary for optimal interaction of the cytochromes c1 with the atypical cytochromes c of these species.

Amino Acid Sequence↗
PubMed1976

Effect of hydroxycobalamin on the inhibition of cytochrome c oxidase by cyanide. II - In isolated cytochrome C oxidase.

The effects of hydroxycobalamin on inhibition of the isolated cytochrome c oxidase (EC 1.9.3.1) by cyanide were studied. No effect of hydroxycobalamin (HCo) and cyanocobalamin (CNCo) was observed on isolated cytochrome c oxidase. When cytochrome c oxidase inhibited by cyanide was treated with HCo the reversal of inhibition could be observed through the spectrum of cytochrome c oxidase without reversal of activity; CNCo had no effect. The treatment of cyano-cytochrome c oxidase with HCo suggests that there is the formation of cobalamin-cytochrome c oxidase complex plus CNCo, and it is possible that complex formation would be between the cobalt of cobalamin and proteic part of cytochrome c oxidase.

Animals↗
PubMed1987

ATP induces conformational changes in mitochondrial cytochrome c oxidase. Effect on the cytochrome c binding site.

ATP influences the kinetics of electron transfer from cytochrome c to mitochondrial oxidase both in the membrane-embedded and detergent-solubilized forms of the enzyme. The most relevant effect is on the so-called "high affinity" binding site for cytochrome c which can be converted to "low affinity" by millimolar concentrations of ATP (Ferguson-Miller, S., Brautigan, D. L., and Margoliash, E. (1976) J. Biol. Chem. 251, 1104-1115). This phenomenon is characterized at the molecular level by the following features. ATP triggers a conformational change on the water-exposed surface of cytochrome c oxidase; in this process, carboxyl groups forming the cluster of negative charges responsible for binding cytochrome c change their accessibility to water-soluble protein modifier reagents; as a consequence the electrostatic field that controls the enzyme-substrate interaction is altered and cytochrome c appears to bind differently to oxidase; photolabeling experiments with the enzyme from bovine heart and other eukaryotic sources show that ATP cross-links specifically to the cytoplasmic subunits IV and VIII. Taken together, these data indicate that ATP can, at physiological concentration, bind to cytochrome c oxidase and induce an allosteric conformational change, thus affecting the interaction of the enzyme with cytochrome c. These findings raise the possibility that the oxidase activity may be influenced by the cell environment via cytoplasmic subunit-mediated interactions.

Adenosine Diphosphate↗
PubMed1988

[Multiple forms of cytochrome P-450. Characteristics of isolated aminopyrine-N-demethylase (cytochrome P-450AP)].

A previously unidentified cytochrome P-450AP possessing the highest aminopyrine-N-demethylase activity has been isolated from liver microsomes of 4-isopropylaminoantipyrine-induced rats, using affinity chromatography in combination with ion-exchange chromatography with subsequent separation on hydroxyl apatite. Using radioisotope techniques, it was found that 4-isopropylaminoantipyrine induces cytochrome P-450AP synthesis de novo. The isolated cytochrome P-450AP has the following characteristics: Mr = 49,000 Da. CO-peak maximum at 450.5 mm, rate of aminopyrine demethylation in a reconstituted system-20 nmol HCHO/min/nmol of cytochrome P-450, benzphetamine-15. The hemoprotein synthesis is paralleled with the synthesis of a protein with Mr of 51,000 Da. Immunochemical analysis permitted to identify the latter protein as cytochrome P-450b. It was demonstrated that cytochrome P-450AP does not interact with the antibodies to the major phenobarbital-induced form, i.e., with cytochrome P-450b.

Aminopyrine N-Demethylase↗