Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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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)

1. Techniques and experiments are described concerned with the millisecond kinetics of EPT-detectable changes brought about in cytochrome c oxidase by reduced cytochrome c and, after reduction with various agents, by reoxidation with O2 or ferricyanide. Some experiments in the presence of ligands are also reported. Light absorption was monitored by low-temperature reflectance spectroscopy. 2. In the rapid phase of reduction of cytochrome c oxidase by cytochrome c (less than 50 ms) approx. 0.5 electron equivalent per heme a is transferred mainly to the low-spin heme component of cytochrome c oxidase and partly to the EPR-detectable copper. In a slow phase (less than 1 s) the copper is reoxidized and high-spin ferric heme signals appear with a predominant rhombic component. Simultaneously the absorption band at 655 nm decreases and the Soret band at 444 nm appears between the split Soret band (442 and 447 nm) of reduced cytochrome a. 3. On reoxidation of reduced enzyme by oxygen all EPR and optical features are restored within 6 ms. On reoxidation by O2 in the presence of an excess of reduced cytochrome c, states can be observed where the low-spin heme and copper signals are largely absent but the absorption at 655 nm is maximal, indicating that the low-spin heme and copper components are at the substrate side and the component(s) represented in the 655 nm absorption at the O2 side of the system. On reoxidation with ferricyanide the 655 nm absorption is not readily restored but a ferric high-spin heme, represented by a strong rhombic signal, accumulates. 4. On reoxidation of partly reduced enzyme by oxygen, the rhombic high-spin signals disappear within 6 ms., whereas the axial signals disappear more slowly, indicating that these species are not in rapid equilibrium. Similar observations are made when partly reduced enzyme is mixed with CO. 5. The results of this and the accompanying paper are discussed and on this basis an assignment of the major EPR signals and of the 655 nm absorption is proposed, which in essence is that published previously (Hartzell, C.R., Hansen, R.E. and Beinert, H. (1973) Proc. Natl. Acad. Sci. U.S. 70, 2477-2481). Both the low-spin (g=o; 2.2; 1.5) and slowly appearing high-spin (g=6; 2) signals are attributed to ferric cytochrome a, whereas the 655 nm absorption is thought to arise from ferric cytochrome a3, when it is present in a state of interaction with EPR-undectectable copper. Alternative possibilities and possible inconsistencies with this proposal are discussed.
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PMID:Kinetic studies on cytochrome c oxidase by combined epr and reflectance spectroscopy after rapid freezing. 0 21

1. The thermodynamics and molecular basis of energy-linked conformational changes in the cytochrome aa3 and ATP synthetase complexes of the mitochondrial membrane have been studied with spectrophotometrical and fluorometrical techniques. 2. Ferric cytochrome aa3 exists in two conformations, high spin and low spin, the equilibrium between these states being controlled by the electrical potential difference across the mitochondrial membrane. The conformational change is brought about by an electrical field-driven binding of one proton per aa3 to the complex. At pH 7.2 the concentration of the two conformations is equal at a membrane potential of 170 mV corresponding to about 4 kcal/mole. 3. The high to low spin transition in ferric aa3 is also induced by hydrolysis of ATP in which case two molecules of aa3 are shifted per ATP molecule hydrolyzed. This is in accordance with translocation of two protons across the mitochondrial membrane coupled to hydrolysis of ATP as proposed in the chemiosmotic theory of oxidative phosphorylation. 4. The conformational transition in cytochrome aa3 is not an expression of the formation of a 'high-energy' intermediate or reversal of the energy-transducing pathway of oxidative phosphorylation, but is presumably the basis of allosteric control of the activity of cytochrome oxidase by the energy state of the mitochondrion. This control is exerted by a regulatory mechanism in which the electrical potential difference controls the conformation and redox properties of the heme centres and thereby the rate of oxygen consumption. 5. The synthesis of one molecule of ATP by oxidative phosphorylation is energetically equivalent to the work done in carrying two electrical charges across the entire mitochondrial membrane. 6. Fluorescence changes of aurovertin bound to ATP synthetase reveal that the electrical membrane potential induces a conformational change in the F1 portion of the enzyme which is probably associated with dissociation of the natural F1 inhibitor protein. This conformational change is energetically equivalent to the work done in carrying one electrical charge across the mitochondrial membrane. 7. A model is proposed for the mechanism of the electrical field-induced conformational changes in the cytochrome aa3 and ATP synthetase complexes, and the significance of these changes in the mechanism and control of mitochondrial energy conservation is discussed.
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PMID:Conformational changes in cytochrome aa3 and ATP synthetase of the mitochondrial membrane and their role in mitochondrial energy transduction. 0 67

The cytochrome oxidase (EC 1.9.3.1) of Rhodopseudomonas palustris was extracted with Triton X-100 plus KCl, from the membrane fraction of cells grown aerobically in the dark. The solubilized enzyme was purified by (NH4)2SO4 precipitation and chromatography on DEAE-cellulose. The purification resulted in a 108-fold enrichment of cytochrome oxidase on the basis of specific activity when compared to the membrane fraction. The purified enzyme was phosphate-sensitive (less than mM), oxidized reduced bovine, horse and yeast cytochrome c, and was inhibited 50% by 0.5 muM KCN or 7 muM NaN3. The native purified preparation migrated as one band in polyacrylamide gel electrophoresis. In the presence of dodecylsulfate four major polypeptides with apparent molecular weights of 30500, 25500, 12200 and 9500 were observed. The enzyme reacted with oxygen via cytochrome o. The purified preparation contained cytochrome c but was free of flavoproteins and NADH-linked and succinate-linked enzyme activities of the respiratory chain.
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PMID:Isolation and partial characterization of the cytochrome oxidase from Rhodopseudomonas palustris. 0 86

A study of the near-infrared absorption spectra of three oxygen compounds of membrane-bound cytochrome oxidase (ferrocytochrome c:oxygen oxidoreductase; EC 1.9.3.1) shows that the formation of compound A (oxycytochrome oxidase) causes no significant infrared absorbance changes at -103 degrees. At -64 degrees, the formation of compound C from the mixed-valence state of the oxidase leads to increased absorption at 740-750 nm. The formation of compound B at -84 degrees from the fully reduced state of the oxidase causes increased absorption at 790-800 nm. Further oxidation of cytochrome oxidase results in increased infrared absorption at 820-830 nm at -60 degrees. The position of the infrared absorption band in compound C thus depends at least upon the oxidation-reduction state of heme a and its associated copper atom. Compound C contains two types of oxidized (cupric) copper; that associated with heme a is initially oxidized, and that associated with heme a3 is oxidized as a second step in the reaction with oxygen. Compound C exhibits a unique intense absorption band at 606-609 nm that is tentatively assigned to a charge transfer interaction between heme a3 in the reduced state and its associated copper in the oxidized state, with heme a and its associated copper in the oxidized state.
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PMID:Oxygen intermediates and mixed valence states of cytochrome oxidase: infrared absorption difference spectra of compounds A, B, and C of cytochrome oxidase and oxygen. 2 80

A study of post-mortem changes in human central nervous tissue has shown that within 100 h of death, no significant change occurs in the amount of nerve cell DNA and nucleolar RNA nor in some membrane-associated enzymes such as succinate dehydrogenase, NADH and NADPH diaphorase, and cytochrome oxidase. Low molecular weight RNA species, probably transfer and messenger RNA are quickly lost, but there is little alteration in ribosomal RNA content. Cytoplasmic enzymes show variable changes; phosphofructokinase activity is rapidly decreased; hexokinase is unaltered but lactate dehydrogenase, pyruvate kinase and glucose-6-phosphate dehydrogenase initially show increases in activity which subsequently decline. Oxygen uptake diminishes quickly. These findings indicate that mechanical alterations in cell structure, following death, render organelles physiologically ineffective long before any significant changes in certain constituent biochemicals are detected. This report emphasizes the great importance necessary in the selection of appropriately time matched post-mortem tissues if accurate comparative studies of many of the cells constituents are to be made.
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PMID:Post-mortem changes in human central nervous tissue and the effects on quantitation of nucleic acids and enzymes. 14 55

1. By the application of the principle of the sequential fragmentation of the respiratory chain, a simple-method has been developed for the isolation of phospholipid-depleted and phospholipid-rich cytochrome oxidase preparations. 2. The phospholip-rich oxidase contains about 20% lipid, including mainly phosphatidylethanolamine, phosphatidylcholine, and cardiolipin. Its enzymic activity is not stimulated by an external lipid such as asolectin. 3. The phospholipid-depleted oxidase contains less than 0.1% lipid. It is enzymically inactive in catalyzing the oxidation of reduced cytochrome c by molecular oxygen. This activity can be fully restored by asolectin; and partially restored (approximately 75%) by purified phospholipids individually or in combination. The activity can be partially restored also by phospholipid mixtures isolated from mitochondria, from the oxidase itself, and from related preparations. Among the detergents tested only Emasol-1130 and Tween 80 show some stimulatory activity. 4. The phospholipid-depleted oxidase binds with cytochrome c evidently by "protein-protein" interactions as does the phospholipid-rich or the phospholipid-replenished oxidase to form a complex with the ratio of cytochrome c to heme a of unity. The complex prepared from phospholipid-depleted cytochrome oxidase exhibits a characteristic Soret absorption maximum at 415 nm in the difference spectrum of the carbon monoxide-reacted reduced form minus the reduced form. This 415-nm maximum is abolished by the replenishment of the complex with a phospholipid or by the dissociation of the complex in cholate or in a medium of high ionic strength. When ascorbate is used as an electron donor, the complex prepared from phospholipid-depleted cytochrome oxidase does not cause the reduction of cytochrome a3 which is in dramatic contrast to the complex from the phospholipid-rich or the phospholipid-replenished oxidase. However, dithionite reduces cytochrome a3 in all of the preparations of the cytochrome c-cytochrome oxidase complex. These facts suggest that the action of phospholipid on the electron transfer in cytochrome oxidase may be at the step between cytochromes a and a3. This conclusion is substantiated by preliminary kinetic results that the electron transfer from cytochrome a to a3 is much slower in the phospholipid-depleted than in phospholipid-rich or phospholipid-replenished oxidase. On the basis of the cytochrome c content, the enzymic activity has been found to be about 10 times higher in the system with the complex (in the presence of the replenishedhe external medium unless energy is provided, and that
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PMID:Studies on cytochrome oxidase. Interactions of the cytochrome oxidase protein with phospholipids and cytochrome c. 16 52

The content of cytochromes a,b and c, the activity of marker enzymes of the matrix and inner membrane of the mitochondria: glutamate dehydrogenase and cytochrome oxidase, as well as the rate of absorption of O2 by root segments in the presence of respiratory substrates, oxygen, inhibitors of respiration, and dinitrophenol, were determined. The intensification of cell respiration in the phase of elongation is determined not so much by new formation of cytochrome components of the respiratory cycle (during this period there is an accumulation only of cytochrome c) as by reorganization of the respiratory cycle (primarily its portion NADH - cytochrome b) and synthesis of enzymes of the matrix.
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PMID:Formation of the enzymatic apparatus of respiration in growing cells. Communication II. Reorganization of the respiratory cycle of mitochondria in the corn root tip. 16 96

Myocardial mitochondrial function and high energy phosphate levels were measured in normal swine, in swine after either 5 or 10 minutes of ischemic ventricular fibrillation (IVF) while on cardiopulmonary bypass, and in swine defibrillated after either 5 or 10 minutes of IVE. The damage to myocardial mitochondria induced by IVF, such as partial uncoupling, decreased oxygen uptake, and loss of cytochrome oxidase activity, was completely reversed almost instantly by coronary artery perfusion and the restoration of sinus rhythm. After either 5 or 10 minutes of IVF followed by coronary artery reperfusion and defibrillation, myocardial creatine phosphate (CP), adenosine monophosphate (AMP) and adenosine diphosphate (ADP) return to normal levels very rapidly. However, adenosine triphosphate (ATP) levels remain significantly lower than control levels. If the bioenergetic mechanisms of swine and human myocardium are similar, it appears that IVF at least for a 10 minute period produces no damage to myocardial mitochondria that is not corrected by perfusion of the coronary arteries and re-establishment of sinus rhythm. Furthermore, sinus rhythm can be re-established and maintained despite signficantly lower levels of myocardial ATP.
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PMID:Restoration of myocardial bioenergetic metabolism in swine after periods of ischemic ventricular fibrillation. 16 32

The development of a low temperature kinetic method for the flash photolysis of the compounds of membrane-bound cytochrome a3 with carbon monoxide in the presence of oxygen affords evidence for three categories of functional intermediate compounds of cytochrome a3 and oxygen. The three classes are identified as follows: Compounds of Type A are considered to be "oxy" compounds of the ferrous heme. They have the composition a3-2+. O2. Compounds of Type B are considered to be peroxide compounds (CU-2+A3-3+ O-2= or CU-2+A3-3+ O2H2) or the equivalent heme Fe-Cu peroxide bridge structures. Compounds of Type C are formed from the ferricyanide pretreated oxidase and may involve higher oxidation states of the heme iron such as quadrivalent iron, and peroxide. Kinetic and equilibrium studies show these compounds to be functional in oxygen reduction in the sequence A yields B yield cytochromes a, c, c1, etc.
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PMID:Functional intermediates in reaction of cytochrome oxidase with oxygen. 16 19

In stopped-flow experiments in which oxidized cytochrome c oxidase was mixed with ferrocytochrome c in the presence of a range of oxygen concentrations and in the absence and presence of cyanide, a fast phase, reflecting a rapid approach to an equilibrium, was observed. Within this phase, one or two molecules of ferrocytochrome were oxidized per haem group of cytochrome a, depending on the concentration of ferrocytochrome c used. The reasons for this are discussed in terms of a mechanism in which all electrons enter through cytochrome a, which, in turn, is in rapid equilibrium with a second site, identified with 'visible' copper (830 nm-absorbing) Cud (Beinert et al., 1971). The value of the bimolecular rate constant for the reaction between cytochromes c2+ and a3+ was between 10(6) and 10(7) M(-1)-S(-1); some variability from preparation to preparation was observed. At high ferrocytochrome c concentrations, the initial reaction of cytochrome c2+ with cytochrome a3+ could be isolated from the reaction involving the 'visible' copper and the stoicheiometry was found to approach one molecule of cytochrome c2+ oxidized for each molecule of cytochrome a3+ reduced. At low ferrocytochrome c concentrations, however, both sites (i.e. cytochrome a and Cud) were reduced simultaneously and the stoicheiometry of the initial reaction was closer to two molecules of cytochrome c2+ oxidized per molecule of cytochrome a reduced. The bleaching of the 830 nm band lagged behind or was simultaneous with the formation of the 605 nm band and does not depend on the cytochrome c concentration, whereas the extinction at the steady-state does. The time-course of the return of the 830 nm-absorbing species is much faster than the bleaching of the 605 nm-absorbing component, and parallels that of the turnover phase of cytochrome c2+ oxidation. Additions of cyanide to the oxidase preparations had no effect on the observed stoicheiometry or kinetics of the reduction of cytochrome a and 'visible' copper, but inhibited electron transfer to the other two sites, cytochrome a3 and the undetectable copper, Cuu.
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PMID:Kinetic studies on the reaction between cytochrome c oxidase and ferrocytochrome c. 16 79


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