The isolation of bovine-heart cytochrome c oxidase subunits. Dependence on phospholipid and cholate-content

Diagnosis of cyanide intoxication by measurement of cytochrome c oxidase activity

Cytochrome c oxidase (CCO), a mitochondrial enzyme, is inactivated by cyanide or carbon monoxide (CO) intoxication. We measured CCO activity, in the major organs of the rat at various times after death caused by cyanide intoxication. Tissue samples were homogenized, and the CCO activity in the mitochondrial fraction was measured using ferrous cytochrome c as the substrate. The CCO activity inhibition was highest in the brain, although the cyanide concentration was lowest level. As a result of this and the clinical symptoms displayed, we consider the brain to be the primary organ of cyanide intoxication. As cyanide is highly toxic to humans, in small amounts and many patients and victims have already had some medical care, it is difficult to detect cyanide in criminal investigations. The CCO activities in various organs remained significantly low for 2 days after the cyanide intoxication, suggesting that the diagnosis may be possible by measuring not only the cyanide concentration but also the CCO activity.

Postmortem changes in cytochrome c oxidase activity in various organs of the rat and in human heart

Cytochrome c oxidase (COX), a mitochondrial enzyme, is inactivated by cyanide or carbon monoxide (CO) intoxication. To test whether cytochrome c has potential as an indicator of these toxins in cadavers, we measured COX activity in the main organs of the rat, and in the human heart, at various times after death. Each tissue sample or organ was homogenized and the COX activity in the mitochondrial fraction was measured using ferrous cytochrome c as the substrate. COX activity was significantly higher in rat brain, heart and kidney than in lung and liver from 0 to 4 days after death. The loss of COX activity was significantly slower in the brain and heart than in the lung, liver and kidney. Most importantly, COX activity correlated with the time-since-death for each of the rat organs we tested (r2=0.70-0.95), but for the human heart (r2=0.47). It may be possible that COX activity is likely to be a useful indicator of the time-since-death, and is worth pursuing as an indicator of the tissue cyanide and CO content.

Dimethyl sulfoxide elicited increase in cytochrome oxidase activity in rat liver mitochondria in vivo and in vitro

A single intraperitoneal injection of dimethyl sulfoxide (275 mg/100 g body wt.) to rats stimulated cytochrome oxidase activity in liver mitochondria 2-5-fold. The enzyme activity remained at this level for as long as 5 days post-injection. There was however only 10.5% increase in the content of cytochromes a and a3 (as determined spectrophotometrically) in the same period in response to DMSO injection. The addition of either DMSO or dimethyl sulfate (a metabolite of DMSO) to isolated liver mitochondria also caused 2-3-fold increase in cytochrome oxidase activity. The results indicate that enhancement in cytochrome oxidase activity in liver mitochondria after administration of DMSO to rats is on account of activation of cytochrome oxidase caused by structural alterations in mitochondrial membranes rather than de novo synthesis of cytochrome oxidase.

The effect of cytochrome c oxidase on lipid polymorphism of model membranes containing cardiolipin

The effect of cytochrome c oxidase incorporation on the lipid polymorphism of the cardiolipin-Ca2+ system was investigated by 31P NMR and freeze-fracture electron microscopy. The integral membrane protein has a stabilizing effect on the bilayer organization of cardiolipin, in that it inhibits the Ca2+-induced HII phase formation of this lipid for Ca2+/cardiolipin molar ratios of 1-10. At a Ca2+/cardiolipin molar ratio of 25, about 80% of the lipid is organized in the HII phase and a structural phase separation occurs between the cardiolipin-Ca2+ complex organized in the hexagonal HII phase without protein and bilayer structures with incorporated protein.

Studies on cytochrome c oxidase, XII. Isolation and primary structure of polypeptide VIb from bovine heart

The isolation and complete sequence analysis of the cytoplasmically synthesized polypeptide VIb from bovine heart cytochrome c oxidase is described. The protein is a stoichiometric constituent of the respiratory complex IV. Its primary structure is deduced from N-terminal sequencing and overlapping peptides obtained from tryptic cleavage and specific cleavage at arginyl and tryptophyl peptide bonds. The polypeptide chain consists of 84 amino acids from which a Mr of 9419 is derived. It has a relatively high content of histidine and proline and contains a single cysteine. A hydrophobic sequence of 20 amino acids points to a membrane-penetrating structure similar to that found in polypeptides I, II, III, IV and VIIIa, VIIIb, VIIIc of the bovine oxidase. The sequence of VIb is tissue-specific, it contributes to the formation of nuclear coded isoenzymes of cytochrome c oxidase. The protein thus may be involved in a tissue-specific regulation of cellular respiration.

The protein formula of beef heart cytochrome c oxidase

Beef heart cytochrome c oxidase consist of 12 different polypeptides stoichiometrically arranged in respiratory complex IV. The functional 2 heme a, 2 copper monomer of this complex consist of 1793 amino acids; the exact Mr is 202,787 Da. From 17 cysteine residues, six are involved in the formation of three disulphide bonds. The theoretical heme a content of the enzyme is 9.86 nmol/mg protein. The theoretical iron and copper contents are 0.55 and 0.63 microgram/mg protein, respectively.

Interactions in cytochrome oxidase: functions and structure

Mitochondrial cytochrome c oxidase is an exceedingly complex multistructural and multifunctional membranous enzyme. In this review, we will provide an overview of the many interactions of cytochrome oxidase, stressing developments not covered by the excellent monograph of Wikström, Krab, and Saraste (1981), and continuing into early 1983. First we describe its functions (both in the nominal sense, as a transporter of electrons between cytochrome c and oxygen, and in its role in energy transduction). Then we describe its structure, emphasizing the protein (its structure as a whole, the number and stoichiometry of its subunits, their biosynthetic origin, and their interactions with each other, with other components of the enzyme complex, and with the membrane as a whole). Finally, we present a model in which the protein conformation serves as the focus for the dynamic interaction of its two major functions.

Arrangement of subunit IV in beef heart cytochrome c oxidase probed by chemical labeling and protease digestion experiments

The arrangement of subunit IV in beef heart cytochrome c oxidase has been explored by chemical labeling and protease digestion studies. This subunit has been purified from four samples of cytochrome c oxidase that had been reacted with N-(4-azido-2-nitrophenyl)-2-aminoethyl[35S]-sulfonate (NAP-taurine), diazobenzene[35S]sulfonate, 1-myristoyl-2-[12-[(4-azido-2-nitrophenyl)amino]lauroyl]-sn-glycero-3- [14C]phosphocholine (I), and 1-palmitoyl-2-(2-azido-4-nitrobenzoyl)-sn-glycero-3-[3H]phosphocholine (II), respectively. The labeled polypeptide was then fragmented by cyanogen bromide, at arginyl side chains with trypsin (after maleylation), and the distribution of the labeling within the sequence was analyzed. The N-terminal part of subunit IV (residues 1-71) was shown to be heavily labeled by water-soluble, lipid-insoluble reagents but not by the phospholipid derivatives. These latter reagents labeled only in the region of residues 62-122, containing the long hydrophobic and putative membrane-spanning stretch. Trypsin cleavage of native cytochrome c oxidase complex at pH 8.2 was shown to clip the first seven amino acids from subunit IV. This cleavage was found to occur in submitochondrial particles but not in mitochondria or mitoplasts. These results are interpreted to show that subunit IV is oriented with its N terminus on the matrix side of the mitochondrial inner membrane and spans the membrane with the extended sequence of hydrophobic lipid residues 79-98 buried in the bilayer.

The reactivity of thiol groups in bovine heart cytochrome c oxidase towards 5,5'-dithiobis(2-nitrobenzoic acid)

Bovine heart cytochrome c oxidase consists of 12 stoicheiometric polypeptide chains of at least 11 different types. The enzyme contains 14--16 cysteine residues; the distribution of nearly all cysteine residues over the subunits has been established. In native cytochrome c oxidase two thiol groups reacted rapidly and stoicheiometrically with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB). These thiol groups are located in subunits I and III, respectively. This implies that subunit I is not fully buried in the hydrophobic core of the enzyme. After dissociation of the enzyme by sodium dodecyl sulphate more thiol groups became available to DTNB, in addition to those in subunits I and III, at least one in subunit II, two in fraction V/VI and one to two in the smallest subunit fraction. It is shown that separation of the subunits of cytochrome c oxidase by gel permeation chromatography in the presence of sodium dodecyl sulphate depends on the pH of the elution medium. The elution volume of subunits I, III and VII is dependent on pH, that of the others independent.

Kinetic and structural differences between cytochrome c oxidases from beef liver and heart

1. The cytochrome content of beef liver mitochondria differs from that of beef heart mitochondria by an eightfold lower cytochrome aa3 and a twofold lower cytochrome b and c + c1 content. 2. The kinetic properties of cytochrome c oxidases from beef liver and heart were measured with intact cytochrome c-depleted membranes, deoxycholate-dissolved membranes, and with the isolated enzymes at various cytochrome c concentrations with an oxygen electrode. Under all conditions a higher V was found for the liver enzyme, both for the low-affinity and for the high-affinity binding site for cytochrome c. Differences were also found for the Km of the two enzymes. 3. Isolated beef heart mitochondria contained about twice as much cardiolipin than beef liver mitochondria. The isolated enzymes contained one mole cardiolipin per mole of the heart enzyme, but 2 moles cardiolipin per mole of the liver enzyme. 4. By application of a high performance sodium dodecylsulfate gel electrophoretic system the two isolated enzymes could be separated into 13 different protein components, three of which (polypeptides VIa, VIIa and VIII) were found to differ in their apparent molecular weights. The functional meaning of cytochrome c oxidase isoenzymes in liver and heart is discussed.

Ion-exchange chromatography in the presence of the non-ionic dissociating agent chloral hydrate. Application to a membrane protein, bovine heart cytochrome c oxidase

In previous work we have shown that aq. 100% (w/v) chloral hydrate (2,2,2-trichloroethane-1,1-diol) is a potent non-ionic protein dissociating agent. We have employed it in systems of polyacrylamide-gel electrophoresis and have demonstrated the presence of 15 components in a preparation of bovine heart cytochrome c oxidase [Griffin & Landon (1981) Biochem. J. 197, 333-344]. Here we describe the use of solutions containing aq. 100% (w/v) chloral hydrate in the ion-exchange column chromatographic separation on CM-cellulose of the alpha- and beta-chains of human haemoglobin, which we have employed as a model protein of known structure. We also describe the use of similar procedures in order to fractionate the polypeptide components of bovine heart cytochrome c oxidase. An effective separation has been obtained and we suggest that chloral hydrate-containing solutions could have general application in the ion-exchange-chromatographic analysis of membrane proteins, a procedure that has had restricted use owing to the inadequacy of non-ionic dissociating agents available previously.

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.

Immunological and chemical characterization of rat liver cytochrome c oxidase

Rat liver cytochrome c oxidase (ferrocytochrome c: oxygen oxidoreductase; EC 1.9.3.1) was separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis into 12 different polypeptide chains. Specific antisera against the holoenzyme and against purified subunits IV and VIII were used to characterize the enzyme complex. The antiserum against subunit IV precipitates from sodium dodecyl sulfate-dissociated mitochondria only subunit IV and from Triton X-100-dissolved mitochondria all 12 polypeptide chains, indicating their integral location within the enzyme complex. Different antisera against the holoenzyme only precipitate subunits IV, V and VIb from sodium dodecyl sulfate-dissociated mitochondria, suggesting the location of these subunits on the surface layer of the complex. Subunit VIII is thought to be located within the complex, since a specific antiserum does not precipitate the complex. The amino acid composition of all 12 protein subunits is different, thus excluding their origin from proteolytic degradation. The proteolytic degradation of subunit IV into IV during isolation of the enzyme was corroborated by the very similar amino acid composition of both proteins.

Proton pump coupled to cytochrome c oxidase in Paracoccus denitrificans

The proton translocating properties of cytochrome c oxidase in whole cells of Paracoccus denitrificans have been studied with the oxidant pulse method. leads to H+/2e- quotients have been measured with endogenous substrates, added methanol and added ascorbate (+TMPD) as reductants, and oxygen and ferricyanide as oxidants. It was found that both the observed leads to H+/O with ascorbate (+TMPD) as reductant, and the differences in proton ejection between oxygen-and ferricyanide pulses, with endogenous substrates or added methanol as a substrate, indicate that the P. denitrificans cytochrome c oxidase translocates protons with a stoichiometry of 2H+/2e-. The results presented in this and previous papers are in good agreement with recent findings concerning the mitochondrial cytochrome c oxidase, and suggest unequal charge separation by different coupling segments of the respiratory chain of P. denitrificans.

Studies on the resolution of cytochrome oxidase

Cytochrome oxidase has been resolved in acetic acid and high salt/detergent media. In 0.5% acetic acid, the smaller subunits of the enzyme are selectively extracted with retention of an insoluble protein fraction containing subunits I-IV, VII. This fraction retains all the heme and copper of the original enzyme in a spectrally unaltered state, and possesses enzymic activity comparable to the unresolved enzyme. The further removal of subunit IV from this fraction results in migration of heme and copper and modification of their spectral characteristics. Resolution of the enzyme in a high salt/detergent medium extracts smaller subunits (V-VII) together with subunit IV and some heme and copper. The heme associated with this enzymically active extract has spectral characteristics that are partially suggestive of heme a3. It is suggested that the fraction of subunits I-IV,VII, resolved in dilute acetic acid, may represent the limit of resolution of the cytochrome oxidase complex that remains actively and spectrally indistinguishable from the original enzyme.

A comparison of the respiratory chain in particles from Paracoccus denitrificans and bovine heart mitochondria by EPR spectroscopy

A study is presented on the EPR characteristics of the paramagnetic groups in the respiratory chain present in membrane particles of Paracoccus denitrificans, the respiratory system of which is very similar to that in submitochondrial particles from beef heart. All paramagnetic prosthetic groups of the mitochondrial system are also found in the bacterial plasma membrane. Their properties suggest that the respiratory groups are embedded in very similar protein environments in the two systems.