Additional components of bovine heart cytochrome c oxidase demonstrated by high-resolution polyacrylamide-gel electrophoresis in the presence of chloral hydrate.

We have shown that aq. 100% (w/v) chloral hydrate (2,2,2-trichloroethane-1,1-diol) dissociates bovine heart cytochrome c oxidase. We have developed new procedures of polyacrylamide-gel electrophoresis in the presence of chloral hydrate that permit variation in the pH of the separation, and, by using these procedures, we have observed 15 components in preparations of the enzyme. This number contrasts with the eight bands that were seen on electrophoresis in the presence of SDS (sodium dodecyl sulphate) and urea. We have isolated material from these eight bands and have characterized each by electrophoresis in the presence of chloral hydrate. Twelve of the fifteen components that were seen by electrophoresis in chloral hydrate were identified as constituents of the eight bands seen by electrophoresis in the presence of SDS and urea. Two-dimensional electrophoretic separations confirmed these identifications ans showed that the other three components which were resolved as discrete bands by electrophoresis in the presence of chloral hydrate appeared to be diffusely present in the electrophoretic separations performed in the presence of SDS and urea, which suggested anomalous behaviour in that detergent. Trypsin treatment of cytochrome c oxidase caused total loss, as observed by electrophoretic separations in the presence of chloral hydrate, of a number of components. The trypsin-sensitive components included all of those that behaved anomalously in the presence of SDS and urea. Chloral hydrate is a potent non-ionic dissociating agent for cytochrome c oxidase and its use in polyacrylamide-gel electrophoresis, with variation in the pH of the gel, permits charge-dependent separations that should have general application in the analysis of membrane proteins.     

Polypeptide components of bovine heart cytochrome c oxidase. Cross-identifications in two high-resolution polyacrylamide-gel electrophoresis systems

Two-dimensional polyacrylamide-gel electrophoresis has been used to correlate polypeptide components of bovine heart cytochrome c oxidase that are resolved by two high resolution systems. The systems utilise chloral hydrate (2,2,2-trichloroethane-1,1-diol), which resolves fifteen components, and sodium dodecyl sulphate and urea, which resolves thirteen components. Seven components have been isolated and identified from their amino acid compositions in terms of polypeptides for which the amino acid sequence is known. Full resolution of all components present in this enzyme cannot be accomplished using any single-dimension system currently available.     

Kinetics of the interaction of the cytochrome c oxidase of Paracoccus denitrificans with its own and bovine cytochrome c

We have devised a relatively simple method for the purification of cytochrome aa3 of Paracoccus denitrificans with three major subunits similar to those of the larger subunits of the mitochondrial cytochrome oxidase. This preparation has no c-type cytochrome. Studies were made of the oxidation of soluble cytochromes c from bovine heart and Paracoccus. The cytochrome-c oxidase activity was stimulated by low concentrations of either cytochrome c, providing an explanation for the multiphasic nature of plots of v/S versus v. Kinetics of the oxidation of bovine cytochrome c by the Paracoccus oxidase resembled those of bovine oxidase with bovine cytochrome c in every way; the Paracoccus oxidase with bovine cytochrome c can serve as an appropriate model for the mitochondrial system. The kinetics of the oxidation of the soluble Paracoccus cytochrome c by the Paracoccus oxidase were different from those seen with bovine cytochrome c, but resembled the latter if poly(L-lysine) was added to the assays. The important difference between the two species of cytochrome c is the more highly negative hemisphere on the side of the molecule way from the heme crevice in the Paracoccus cytochrome. Thus, the data emphasize the importance of all of the charged groups on cytochrome c in influencing the binding or electron transfer reactions of this oxidation-reduction system. The data also permit some interesting connotations about the possible evolution from the bacterial to the mitochondrial electron transport system.     

Chloral hydrate anesthesia alters cerebral enzymes in the rat. A histochemical study

Cerebral forebrain arterioles and neuropil were analyzed histochemically to determine the effects of chloral hydrate anesthesia on key enzymes of aerobic and anaerobic metabolism, as well as the hexose monophosphate shunt in rats. Significant decreases were observed in cytochrome oxidase, and beta-hydroxybutyrate dehydrogenase in arterioles, while glucose-6-phosphate dehydrogenase and isocitric dehydrogenase showed a significant increase and lactate dehydrogenase showed no significant change. In the neuropil, cytochrome oxidase, isocitrate dehydrogenase and glucose-6-phosphate dehydrogenase showed significant increases following chloral hydrate administration, while beta-hydroxybutyrate dehydrogenase and lactate dehydrogenase showed no significant changes. These data suggest that surgical anesthetic levels of chloral hydrate can impair forebrain metabolism which may lead to altered electrophysiological responses.     

Subunits VIIa,b,c of human cytochrome c oxidase. Identification of both 'heart-type' and 'liver-type' isoforms of subunit VIIa in human heart.

The N-terminal amino acid sequences and the electrophoretic mobilities of the subunits VIIa, VIIb and VIIc of cytochrome c oxidase purified from human heart were investigated and compared with those from human skeletal muscle and from bovine heart. In purified human heart cytochrome c oxidase, both so-called 'heart-type' and 'liver-type' isoforms of subunit VIIa were found. The first 30 residues of the N-terminal amino acid sequences of these 'heart-type' and 'liver-type' subunits VIIa showed nine differences. The two isoforms of subunit VIIa in human heart were present in almost equal amounts, in contrast to the situation in skeletal muscle, where the 'heart-type' subunit VIIa was predominant. Therefore, our results imply that in human heart a cytochrome c oxidase isoform pattern is present that differs from that found in skeletal muscle. Subunits VIIb and VIIc purified from human heart oxidase proved to be very similar to their bovine heart counterparts. Our direct demonstration of the presence of subunit VIIb, the sequence of which has only recently been identified in the bovine heart enzyme, suggests that human cytochrome c oxidase also contains 13 subunits. We found no evidence for the presence of different isoforms of subunit VIIc in cytochrome c oxidase from human heart and skeletal muscle. We observed clear differences in the electrophoretic mobility of the subunits VIIa,b,c between bovine and human cytochrome c oxidase. On Tricine/glycerol/SDS/polyacrylamide gels the 'heart-type' and 'liver-type' subunits VIIa present in human heart cytochrome c oxidase migrated with almost the same electrophoretic mobility. Subunit VIIb migrated only slightly faster than subunit VIIa, whereas VIIc proved to have the highest electrophoretic mobility on Tricine/SDS/glycerol/polyacrylamide gels. Our findings may have implications for the elucidation of certain tissue-specific cytochrome c oxidase deficiencies in man.     

Molecular state of cy tochrome c oxidase on polyacrylamide gel electrophoresis

The molecular state of cytochrome oxidase, complex IV (EC 1.9.3.1), was studied by polyacrylamide gel electrophoresis. Cytochrome oxidase in the presence of non-ionic detergent Emasol 1130 ran as a single band under conditions where there is a small sieving effect as in a 2.5% polyacrylamide gel. This polymeric form is an association of different molecular species that can be dissociated on a preparative electrophoresis system. In such a system, five species of different molecular size with enzymic activity are obtained, though the specific activity is lower in the first running fractions. After treatment in highly dissociating conditions (phenol-acetic acid-water (2:1:1, w/v/v) the polymeric form and the different species present two main fractions on analytical polyacrylamide electrophoresis (7.5% in acrylamide, 35% acetic acid, and 5 m urea). The original form after treatment with 2.5% sodium dodecylsulfate (SDS) also presents two fractions on analytical electrophoresis in the presence of 2.5% sodium dodecylsulfate. These results suggest that the basic subunit structure of the various forms of the cytochrome oxidase consists of two closely related polypeptides. The highest activity was found with the polymeric form of cytochrome oxidase, a fact which may have physiological significance in relation to the natural state of this enzyme in the mitochondrion.     

Differential effects of chloral hydrate- and ketamine/xylazine-induced anesthesia by the s.c. route

The proper use of anesthetics in animal experimentation has been intensively studied. In this study we compared the use of chloral hydrate (500 mg kg(-1)) and ketamine (167 mg kg(-1)) combined with xylazine (33 mg kg(-1)) by the s.c. route in male Wistar rats. Chloral hydrate and ketamine/xylazine produced a depth of anesthesia and analgesia sufficient for surgical procedures. The decrease of systolic and diastolic blood pressure was of a higher magnitude in rats anesthetized with chloral hydrate than with ketamine/xylazine. The initial microvascular diameter and blood flow velocity did not differ between both agents. On the other hand, ketamine/xylazine reduced the heart rate more intensively than chloral hydrate. Both anesthetics promoted an increase in arterial pCO(2) and a decrease in pH levels compared to unanesthetized animals. The blood glucose levels were of a higher magnitude in rats after ketamine/xylazine anesthesia than after chloral hydrate. In mesenteric arterioles studied in vivo, ketamine/xylazine anesthesia reduced the constrictive effect of noradrenaline and the dilator effect of bradykinin. However, both anesthetics did not modify the vasodilator effect promoted by acetylcholine. Based on our data, we concluded that both anesthetics alter metabolic and hemodynamic parameters, however the use of chloral hydrate in studies of microvascular reactivity in vivo is more appropriate since ketamine/xylazine reduces the responses to vasoactive agents and increases blood glucose levels.     

Similarities and dissimilarities in the structure-function relation between the cytochrome c oxidase from bovine heart and from Paracoccus denitrificans as revealed by FT-IR difference spectroscopy.

The redox dependent changes in the cytochrome c oxidase from bovine heart were studied with a combined electrochemical and FT-IR spectroscopic approach. A direct comparison to the electrochemically induced FT-IR difference spectra of the cytochrome c oxidase from Paracoccus denitrificans reveals differences in the structure and intensity of vibrational modes. These differences are partially attributed to interactions of subunits influencing the heme and protein modes. In the spectral regions characteristic for v(C=O) and v(COO-)s/as modes of protonated and deprotonated Asp and Glu residues, additional signals at 1736, 1602 and 1588 cm-1 are observed. On this basis, the possible involvement of Asp-51, a residue specifically conserved in mammalian oxidase and previously proposed to show redox depended conformational changes in the respective X-ray structures, is critically discussed.     

A Triton X-100-hydroxyapatite procedure for a rapid purification of bovine heart cytochrome-c oxidase. Characterization of the cytochrome-c oxidase/Triton X-100/phospholipid mixed micelles by laser light scattering

Cytochrome-c oxidase (ferrocytochrome-c:oxygen oxidoreductase, EC 1.9.3.1) has been isolated from bovine heart mitochondria by the combined use of the non-ionic detergent Triton X-100 as solubilizing agent and hydroxyapatite chromatography as the most important step in the purification of this membrane protein. This method is fast and very reproducible. The enzymic complex, purified in the form of protein/detergent/phospholipid mixed micelles, contains 9.7 mumol heme a per mg protein, and has a high molecular activity (500 mol cytochrome c per s per mol enzyme). These mixed micelles have been studied by laser light scattering, which has shown that the average molecular weight of the micelles is 540 +/- 80 kDa. This implies that cytochrome-c oxidase is purified in the form of a dimer. The average quadratic radius of gyration of the micelles is 40 +/- 10 nm, corresponding in our case to an approximately spherical shape.     

The nuclear-coded subunits of yeast cytochrome c oxidase. II. The amino acid sequence of subunit VIII and a model for its disposition in the inner mitochondrial membrane

The amino acid sequence of subunit VIII from yeast cytochrome c oxidase is reported. This 47-residue (Mr = 5364) amphiphilic polypeptide has a polar NH2 terminus, a hydrophobic central section, and a dilysine COOH terminus. An analysis of local hydrophobicity and predicted secondary structure along the peptide chain predicts that the hydrophobic central region is likely to be transmembranous. Subunit VIII from yeast cytochrome c oxidase exhibits 40.4% homology to bovine heart cytochrome c oxidase subunit VIIc , at the level of primary structure. Secondary structures and hydrophobic domains predicted from the sequences of both polypeptides are also highly conserved. From the location of hydrophobic domains and the positions of charged amino acid residues we have formulated a topological model for subunit VIII in the inner mitochondrial membrane.     

An obligatory role of protein glycosylation in the life cycle of yeast cells

Two water-soluble carbodiimides, differing in molecular dimensions, have been used to characterize the cytochrome c binding site of bovine heart cytochrome c oxidase. Several polypeptide components of the enzyme contain acidic residues which are modified by these reagents. Carboxyl groups present in subunit II, VII and polypeptide c, are protected from modification when cytochrome c, equimolar to oxidase, is added and they can cross-link to the substrate once activated by the carbodiimide. Comparison of the modification patterns suggest that the most reactive residues are located on subunit II and VII, the former being also more exposed. The data obtained indicate that even though subunit II plays the major role in binding cytochrome c, at least two other lower Mr polypeptides contribute to the cytochrome c binding domain.     

Determination of molecular mass of the aroid alternative oxidase by radiation-inactivation analysis.

The functional molecular mass of the cyanide-resistant salicylhydroxamate-sensitive duroquinol oxidase activity from Sympocarpus foetidus (skunk cabbage) and Sauromatum guttatum spadix mitochondria was determined by radiation-inactivation analysis. The functional molecular mass for the oxidase activity was found to be 26,700 Da for skunk cabbage and 29,700 Da for Sauromatum guttatum mitochondria frozen at -70 degrees C. Irradiation of dried mitochondrial samples resulted in a larger target size of 38,000 Da, and in some cases, a stimulation of activity at low dose of radiation. The functional molecular mass of cytochrome c oxidase activity from skunk-cabbage and bovine heart mitochondria was also investigated. Dried and frozen mitochondrial samples from both species yielded similar target sizes, in the range 70,900-73,400 Da. Purified bovine heart cytochrome c oxidase was also irradiated, and yielded a functional molecular mass of 66,400 Da. The target size of cytochrome c oxidase agrees with literature values insofar as the target size is considerably smaller than the molecular mass of the entire complex.     

Study of the interaction between cytochrome c and cytochrome oxidase by tritium planigraphy

Treatment of molecular crystals of the bovine cytochrome oxidase and the cytochrome oxidase-cytochrome c complex with thermally activated tritium leads to highly labelled cytochrome oxidase preparations. HPLC separation of its subunits and measurements of radioactivity of each polypeptide allow to determine the shielding of cytochrome oxidase surface sites by cytochrome c in the complex.     

Vectorially oriented monolayers of the cytochrome c/cytochrome oxidase bimolecular complex.

Vectorially oriented monolayers of yeast cytochrome c and its bimolecular complex with bovine heart cytochrome c oxidase have been formed by self-assembly from solution. Both quartz and Ge/Si multilayer substrates were chemical vapor deposited with an amine-terminated alkylsiloxane monolayer that was then reacted with a hetero-bifunctional cross-linking reagent, and the resulting maleimide endgroup surface then provided for covalent interactions with the naturally occurring single surface cysteine 102 of the yeast cytochrome c. The bimolecular complex was formed by further incubating these cytochrome c monolayers in detergent-solubilized cytochrome oxidase. The sequential formation of such monolayers and the vectorially oriented nature of the cytochrome oxidase was studied via meridional x-ray diffraction, which directly provided electron density profiles of the protein(s) along the axis normal to the substrate plane. The nature of these profiles is consistent with previous work performed on vectorially oriented monolayers of either cytochrome c or cytochrome oxidase alone. Furthermore, optical spectroscopy has indicated that the rate of binding of cytochrome oxidase to the cytochrome c monolayer is an order of magnitude faster than the binding of cytochrome oxidase to an amine-terminated surface that was meant to mimic the ring of lysine residues around the heme edge of cytochrome c, which are known to be involved in the binding of this protein to cytochrome oxidase.     

Subunit III of cytochrome c oxidase is expressed in Paracoccus denitrificans

Polyclonal antibodies have been obtained against a synthetic dodecapeptide identical to the aminoacid sequence 120-131 DSPIKDGVWPPE (inferred from its DNA sequence) of Paracoccus denitrificans cytochrome c oxidase subunit III. The antibodies had a titer higher than 1:10000 when tested against the antigen. These antibodies have been used to produce immunological evidence that, despite the fact that subunit III is not isolated with cytochrome c oxidase, it exists in Paracoccus denitrificans lysates. The antibodies did not show reactivity with bovine heart cytochrome c oxidase either by ELISA or immunoblotting. It was also shown that the antibodies react with a single polypeptide present in Paracoccus denitrificans cell lysates, having an apparent molecular weight close to that of subunit III of bovine heart oxidase.     

Isoforms of human cytochrome-c oxidase. Subunit composition and steady-state kinetic properties.

The subunit pattern and the steady-state kinetics of cytochrome-c oxidase from human heart, muscle, kidney and liver were investigated. Polyacrylamide gel electrophoresis of immunopurified cytochrome-c oxidase preparations suggest that isoforms of subunit VIa exist, which show differences in staining intensity and electrophoretic mobility. No differences in subunit pattern were observed between the other nucleus-encoded subunits of the various cytochrome-c oxidase preparations. Tissue homogenates, in which cytochrome-c oxidase was solubilised with laurylmaltoside, were directly used in the assays to study the cytochrome-c oxidase steady-state kinetics. Cytochrome-c oxidase concentrations were determined by immunopurification followed by separation and densitometric analysis of subunit IV. When studied in a medium of low ionic strength, the biphasic kinetics of the steady-state reaction between human ferrocytochrome c and the four human cytochrome-c oxidase preparations revealed large differences for the low-affinity TNmax (maximal turnover number) value, ranging from 77 s-1 for kidney to 273 s-1 for liver cytochrome-c oxidase at pH 7.4, I = 18 mM. It is proposed that the low-affinity kinetic phase reflects an internal electron-transfer step. For the steady-state reaction of human heart cytochrome-c oxidase with human cytochrome c, Km and TNmax values of 9 microM and 114 s-1 were found, respectively, at high ionic strength (I = 200 mM, pH 7.4). Only minor differences were observed in the steady-state activity of the various human cytochrome-c oxidases. The interaction between human cytochrome-c oxidase and human cytochrome-c proved to be highly specific. At high ionic strength, a large decrease in steady-state activity was observed when reduced horse, rat or bovine cytochrome c was used as substrate. Both the steady-state TNmax and Km parameters were strongly affected by the type of cytochrome c used. Our findings emphasize the importance of using human cytochrome c in kinetic assays performed with tissues from patients with a suspected cytochrome-c oxidase deficiency.     

Intraliposomal nucleotides change the kinetics of reconstituted cytochrome c oxidase from bovine heart but not from Paracoccus denitrificans

Isolated cytochrome c oxidases of P. denitrificans and bovine heart were reconstituted in liposomes and the kinetics of cytochrome c oxidation were measured in the presence and absence of nucleotides either inside or outside of proteoliposomes, and after photolabelling with 8-azido-ATP. Intraliposomal ATP increases and ADP decreases the kinetics of ferrocytochrome c oxidation of the bovine but not of the Paracoccus enzyme. Extra-liposomal ATP and ADP increase the Km for cytochrome c of both enzymes, but ATP acts at lower concentrations than ADP. The increase of the Km for cytochrome c is obtained in coupled as well as in uncoupled proteoliposomes. Photolabelling with 8-azido-ATP of the reconstituted Paracoccus enzyme also increases the Km for cytochrome c which is completely prevented if ATP but not if ADP is present during illumination as was found with reconstituted cytochrome c oxidase from bovine heart. The data suggest a specific interaction of ATP and ADP with nuclear-coded subunits of bovine heart cytochrome c oxidase from the matrix side, because the effects are not found with the Paracoccus enzyme, which lacks these subunits.     

Inhibition of plant and animal cytochrome oxidases by nitrous oxide as a function of cytochrome c concentration.

Cytochrome oxidase from both pea leaves and bovine heart shows lower activity under a mixture of 79% N2O/21% O2 than under ambient air. This inhibition is not detectable below 5 microM cytochrome c but appears with increasing concentrations of cytochrome c. These results suggest that the N2O-induced inhibition of cytochrome c oxidase is modulated by cytochrome c concentration. This seems to concern only the lowest affinity site of the oxidase. Apparently, N2O and cytochrome c do not share the same site of fixation on the oxidase.     

Human cytochrome c oxidase isoenzymes from heart and skeletal muscle; purification and properties

Human cytochrome c oxidase was isolated in an active form from heart and from skeletal muscle by a fast, small-scale isolation method. The procedure involves differential solubilisation of the oxidase from mitochondrial fragments by laurylmaltoside and KCl, followed by size-exclusion high-performance liquid chromatography. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate showed differences between the subunit VI region of cytochrome c oxidases from human heart and skeletal muscle, suggesting different isoenzyme forms in the two organs. This finding might be of importance in explaining mitochondrial myopathy which shows a deficiency of cytochrome c oxidase in skeletal muscle only. In SDS polyacrylamide gel electrophoresis most human cytochrome c oxidase subunits migrated differently from their bovine counterparts. However, the position of subunits III and IV was the same in the human and in the bovine enzymes. The much higher mobility of human cytochrome c oxidase subunit II is explained by a greater hydrophobicity of this polypeptide than of that of the subunit II of the bovine enzyme.     

Photoinduced intracomplex electron transfer between cytochrome c oxidase and TUPS-modified cytochrome c.

A novel method for initiating intramolecular electron transfer in cytochrome c oxidase is reported. The method is based upon photoreduction of cytochrome c labeled with thiouredopyrene-3,6, 8-trisulfonate in complex with cytochrome oxidase. The thiouredopyrene-3,6,8-trisulfonate-labeled cytochrome c was prepared by incubating the thiol reactive form of the dye with yeast iso-1-cytochrome c, containing a single cysteine residue. Laser pulse excitation of a stoichiometrical complex between thiouredopyrene-3,6,8-trisulfonate-cytochrome c and bovine heart cytochrome oxidase at low ionic strength resulted in the reduction of cytochrome c by the excited form of thiouredopyrene-3,6, 8-trisulfonate and subsequent intramolecular electron transfer from the reduced cytochrome c to cytochrome oxidase. The maximum efficiency by a single laser pulse resulted in the reduction of approximately 17% of cytochrome a, and was achieved only at a 1 : 1 ratio of cytochrome c to cytochrome oxidase. At higher cytochrome c to cytochrome oxidase ratios the heme a reduction was strongly suppressed.