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Query: EC:1.9.3.1 (cytochrome oxidase)
 8,822 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Oxidation of ferrocytochrome c by molecular oxygen catalysed by cytochrome c oxidase (cytochrome aa3) is coupled to translocation of H+ ions across the mitochondrial membrane. The proton pump is an intrinsic property of the cytochrome c oxidase complex as revealed by studies with phospholipid vesicles inlayed with the purified enzyme. As the conformation of cytochrome aa3 is specifically sensitive to the electrochemical proton gradient across the mitochondrial membrane, it is likely that redox energy is primarily conserved as a conformational "strain" in the cytochrome aa3 complex, followed by relaxation linked to proton translocation. Similar principles of energy conservation and transduction may apply on other respiratory chain complexes and on mitochondrial ATP synthase.
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PMID:The mechanism of energy conservation and transduction by mitochondrial cytochrome c oxidase. 20 Dec 86

The luminescent properties of metal-free, tin(IV) and zinc(II) cytochromes c have been used to characterize the interaction of cytochrome c with mitochondria and cytochrome oxidase. Diminution in the fluorescence yields of tin and zinc cytochrome c occur when these derivates bind to cytochrome oxidase or mitochondria. Based upon spectral overlap and quantum yield, the distance between the porphyrin rings of cytochrome a and cytochrome c is estimated according to Forster theory to be in the neighborhood of 3.5 nm. Measurements of the polarized emission of metal-free 'porphyrin' cytochrome c when bound to oriented layers of cytochrome c oxidase indicate that the porphyrin is bound obliquely to the plane of the oxidase layers with an angle of about 70 degrees C from heme plane to membrane plane. It is proposed that these data have significance for elucidation of electron transfer mechanisms.
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PMID:Metal-free and metal-substituted cytochromes c. Use in characterization of the cytochrome c binding site. 20 55

The deuterium magnetic resonance spectra of lipid-protein particles containing cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) isolated from beef heart mitochondria and the specifically deuterated lipid 1-(16,16,16-trideuteropalmitoyl)-2-palmitoleoyl phosphatidylcholine are presented. These reconstituted particles are of uniform lipid and protein content; however, the spectra clearly show two environments characterized by distinctly different residual quadrupolar splittings or order parameters. The less-ordered environment shows a splitting similar to but slightly less than that of the pure lipid alone at a given temperature. The more restricted environment appears to be induced by the presence of the protein. The amount of the restricted lipid is clearly temperature dependent with a 2- to 3-fold decrease in relative amount from 2 to 22 degrees. The rate of exchange of lipid between the free and restricted environments is slower than 10(3)/sec. The significance of these phenomena is discussed.
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PMID:Deuterium magnetic resonance studies of the interaction of lipids with membrane proteins. 20 55

Kinetic studies of the reactions of selected eukaryotic and prokaryotic cytochromes c with mitochondrial cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase (EC 1.9.3.1) using a standardized complex IV preparation from beef heart are reported. Data on reactions with NADH-linked cytochrome c reductase (complexes I and III) are included. The concentration ranges employed provide a basis for quantitative demonstration of a general rate law applicable to oxidase reactions of cytochrome c of greatly differing reactivities. Results are interpreted on the basis of a modified Minnaert mechanism (Minnaert, K. (1961) Biochim. Biophys. Acta 50, 23), assuming productive complex formation between cytochrome c and free oxidase in addition to further complex binding of a second cytochrome c molecule to the initially formed oxidase complex. Kinetic constants so obtained are consistent with the assumption that binding is the dominant parameter in reactivity, and can be rationalized most simply on this basis.
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PMID:Comparative kinetic studies of cytochromes c in reactions with mitochondrial cytochrome c oxidase and reductase. 20 37

Cytochrome c derivatives labeled with a 3-nitrophenylazido group at lysine 13, at lysine 22, or at both residues have been prepared. The interaction of the cytochrome c derivatives with beef heart cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) in the presence of ultrviolet light results in formation of a covalent complex between cytochrome c and the oxidase. Using the lysine 22 derivative, the polypeptide composition of the oxidase is not modified, nor is its catalytic activity, whereas with the lysine 13 derivative, the gel electrophoretic pattern is altered and the catalytic activity of the complex diminished. The data are consisten with a specfic covalent interaction of the lysine 13 derivative of cytochrome c with the polypeptide of molecular weight 23,700 (Subunit II) of cytochrome c oxidase.
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PMID:Interaction of cytochrome c with cytochrome c oxidase. Photoaffinity labeling of beef heart cytochrome c oxidase with arylazido-cytochrome c. 20 34

1. Both valinomycin and p-trifluoromethoxy carbonyl cyanide phenylhydrazone (FCCP) are required for full release of respiration by cytochrome c oxidase-containing proteoliposomes (prepared by sonicating beef heart cytochrome aa3 in salt solution with 4 parts phosphatidylcholine, 4 parts phosphatidylethanolamine and 2 parts cardiolipin) in the presence of external ascorbate and cytochrome c. In the absence of valinomycin the response to FCCP is rather sluggish, as reported by Wrigglesworth et al. (1976) (Abstracts, 10th Int. Congr. Biochem., No. 06-6-230). 2. The Km for cytochrome c in 67 mM, pH 7.4, phosphate buffer with ascorbate as substrate, was 9 micrometer in both absence and presence of valinomycin and FCCP. Energization thus acts non-competitively towards cytochrome c oxidation. 3. The apparent Km for oxygen is greater in the energized than in the deenergized state; double reciprocal plots of respiration rate versus oxygen concentration are concave downward in the absence of uncouplers, as found with intact mitochondria. Energization thus acts "competitively" towards oxygen. 4. Despite the lack of a functional ATPase system, all the kinetic features of energization found in intact mitochondria can be mimicked in the reconstituted liposomes. This supports the chemiosmotic idea that electrical and perhaps H+ gradients modify the oxidase activity in reconstituted vesicles.
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PMID:Control of respiration in proteoliposomes containing cytochrome aa3. I. Stimulation by valinomycin and uncoupler. 20 20

1. Hydrophobic interaction chromatography on Octyl-Sepharose CL-4B is used as a new and simple method for the preparation of large amounts of beef-heart cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1). 2. The method involves only one cycle of (NH4)2SO4 fractionation before the material is applied to the column. After washing with 10% cholate and 1.5% Tween 80, elution of the enzyme is accomplished with 1% Triton X-100. 3. The enzyme so prepared contains about 10 nmol heme alpha/mg protein and about 0.2% phospholipid. 4. Characterization of the enzyme has been made with optical and EPR spectroscopy and polyacrylamide gel electrophoresis. The preparation appears by these criteria to be at least as good as other purified enzyme preparations. 5. The turnover rate at infinite cytochrome c concentration in 0.1 M sodium phosphate buffer and 0.5% Tween 80 at pH 6.1 is 80 s-1 per functional unit of the enzyme. A more than three-fold activation could be obtained by the addition of phosphatidylcholine at neutral pH.
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PMID:Purification of beef-heart cytochrome c oxidase by hydrophobic interaction chromatography on octyl-Sepharose CL-4B. 20 31

The kinetics of CO binding by the cytochrome c oxidase of pigeon heart mitochondria were studied as a function of membrane energization at temperatures from 180 to 280 degrees K in an ethylene glycol/water medium. Samples energized by ATP showed acceleration of CO binding compared to those untreated or uncoupled by carbonylcyanide p-trifluoromethyoxyphenylhydrazone but only at relatively low temperatures and high CO concentrations. Experiments using samples in a "mixed valency" (partially oxidized) state showed that the acceleration of ligand binding is not due to the formation of a partially oxidized state via reverse electron transport. It is concluded that in the deenergized state one CO molecule can be closely associated with the cytochrome a3 heme site without actually being bound to the heme iron; in the energized state, two or more ligand molecules can occupy this intermediate position. The change in the apparent ligand capacity of a region near the heme iron in response to energization is evidence for an interaction between cytochrome oxidase and the ATPase system. Furthermore, these results suggest a control mechanism for O2 binding.
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PMID:The effect of mitochondrial energization on cytochrome c oxidase kinetics as measured at low temperatures. I. The reaction with carbon monoxide. 20 2

The effect of pre-energization of isolated mitochondria by ATP at room temperature upon the kinetics of oxygen intermediates (measured at very low temperatures) of cytochrome c oxidase has been studied. It was found that "energization" of mitochondria at room temperature had dramatic effects on several partial reactions of cytochrome aa3. Thus, in the "energized" frozen state, the rate of O2 binding to ferrous cytochrome a3 and the subsequent formation of the "peroxy" compound B are accelerated, while oxidation of cytochromes c and c1 is inhibited. These effects of ATP are abolished by oligomycin and uncoupling agents and may, therefore, be reflections of the coupling of the mitochondrial ATP synthetase to the respiratory chain at the level of cytochrome c oxidase, which is the basis of the mechanism of coupling respiration to ATP synthesis and respiratory control.
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PMID:The effect of mitochondrial energization on cytochrome c oxidase kinetics as measured at low temperatures. II. The binding and reduction of dioxygen. 20 3

Seven protein subunits of cytochrome c oxidase from bovine heart were isolated by gel filtration in the presence of sodium dodecyl sulphate (subunits I, II and III) and guanidine hydrochloride (subunits V, VI and VII), and ion-exchange chromatography in 6 M urea (subunit IV) after the enzyme had been dissociated in 6 M guanidine hydrochloride. When analysed by highly cross-linked sodium dodecyl sulphate/polyacrylamide gel electrophoresis in the presence of urea, the apparent molecular weights were = I, 36700; II, 24300; III, 20400; IV, 17300; V, 12300; VI, 8700: and VII, 5100. Monospecific rabbit antisera were obtained against subunits I, IV, V, VI and VII and a mixture of subunits II and III. These subunit-specific antisera with the exception of anti-I serum all cross-reacted with the detergent-solubilized native oxidase. Enzymatic studies on purified oxidase indicated that immunoglobulins against subunits II + III, IV, V, VI and VII respectively caused 25, 65, 20, 30 and 25% inhibition while anti-I immunoglobulin did not inhibit the activity. The subunit-specific antisera were used to examine the arrangements of the subunits in the membrane. Enzymatic studies using bovine heart mitochondria and rat liver mitochondrial digitonin particles showed that anti-(II + III) serum, anti-V serum and anti-VII serum all inhibited the oxidase activity while the other antisera did not. On the other hand, results of using 125I-labelled immunoglobulins showed that anti-IV, anti-V and anti-VII sera were bound to the surface of inverted vesicles (matrix side) while all other antisera were not. These results indicate that cytochrome oxidase subunits II and III are situated on the outer surface, and subunit IV is exclusively on the matrix surface while subunits V and VII are exposed on both surfaces of the mitochondrial membrane. Subunits I and VI are buried within the membrane, not exposed on either side.
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PMID:Immunological studies on cytochrome c oxidase: arrangements of protein subunits in the solubilized and membrane-bound enzyme. 21 67


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