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

---

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

Highly active, essentially homogeneous, preparations of ferrocytochrome c oxidase (EC 1.9.3.1) have been obtained from both yeast and beef heart by extraction with cholate, fractionation with ammonium sulfate, and replacement of cholate by Tween 20. The molecular weights of the resultant proteins equal 260 +/- 23 X 10(3) and 205 +/- 10(3); they contain seven and six different polypeptide subunits, respectively, all in equimolar amounts, with apparent molecular weights of 42.4, 34.1, 24.7, 14.6, 14.6, 12.3, 10.6 X 10(3), and 47.5, 20.4, 14.5, 14.5, 13.0, 11.0 X 10(3), respectively. By means of apolar chromatography on L-leucine coupled to agarose these enzymes can be stripped of their largest subunit(s) resulting in preparations with molecular weights of 170 +/- 17 X 10(3) and 124 +/- 20 X 10(3), and containing only five polypeptides, with the largest remaining one (molecular weight congruent to 20 X 10(3)) present in less than stoichiometric amounts. This interconversion and subunit removal has been monitored by exclusion chromatography, four systems of acrylamide gel electrophoresis--some with the protein labeled with 125I under denaturing conditions--isoelectric focusing, and hydrodynamic methods. It has virtually no effect on heme a and copper content and on the catalytic parameters of the enzymes. We conclude that subunits I and II in enzymes from fungal, and subunit I in those from animal, sources are dispensable for the catalysis of the oxidation of ferrocytochrome c by, and are probably not essential for the attatchment of prosthetic groups to, these proteins.
...
PMID:Studies on cytochrome oxidase. Partial resolution of enzymes containing seven or six subunits, from yeast and beef heart, respectively. 0 85

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.
...
PMID:Kinetic studies on cytochrome c oxidase by combined epr and reflectance spectroscopy after rapid freezing. 0 21

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.
...
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

We have previously described a transient high spin ferric heme species in cytochrome c oxidase (EC 1.9.3.1) which represent a3+(3) (Beinert, H. and Shaw, R.W.(1977) Biochim. Biophys. Acta 462, 12u--130), and can be detected and quantitatively determined by EPR. We have now used out ability to generate this species to study reactions of a3+(3) with substrates and ligands and also responses to pH changes. This was accomplished by multiple rapid mixing and freezing techniques in conjunction with low temperature EPR and optical reflectance spectroscopies. The substrates used were O2 and ferrocytochrome c and the ligands cyanide, sulfide, azide and carbon monoxide. Contrary to the oxidized, resting form of the enzyme, the transient high spin species of a3+(3) reacts within less than 10 ms stoichiometrically with cyanide and sulfide and at a slower rate with azide. The transient a3+(3) species responds to O2 and CO by changes in signal size or shape, although no oxidoreduction is involved, indicating that a3+(3) registers the presence of these gases. The high spin signal of the transient species is readily abolished by ferrocytochrome c or on raising the pH. Decreasing the pH induces a shift from the rhombic towards the axial component of the signal. Since the responses to CO and pH are analogous for the rhombic transient species to those observed with the rhombic high spin ferric heme species produced on partial reduction, it is suggested that the rhombic signals represent a3+(3) in either case. In all these experiments, in which EPR detectable a3+(3) was observed in large yield, no extra signals for copper or correspondingly increased intensity in the copper signal at g = 2 were seen. The relationship is discussed of the obviously reactive transient species of a3+(3) to other 'activated' species that have been reported and to the oxidized resting form of the enzyme, which is known to react only slowly with ligands and to respond sluggishly to substrate.
...
PMID:Responses of the a3 component of cytochrome c oxidase to substrate and ligand addition. 3 Apr 77

The pH-induced dissociation of cytochrome c oxidase from dimer to protomer has been studied in the pH range 7 to 11. Findings are as follows: The heme A:copper ratio is 1.0 at both pH 7.4 and 10.6. The relative enzymatic activity is preserved at all pH values at which the dimer or protomer are found. The fraction of protomer, determined from sedimentation velocity profiles, increases from 0 to 1 as the pH is raised. The absorption and circular dichroism spectra in the Soret region change in ways indicating that the contributions of cytochrome a in typical cytochrome aa3 spectral patterns are progressively lost as pH increases. At pH values more alkaline than the above, denaturation occurs. The fraction of protomer, and certain parameters defined to quantitate the changes in spectral form, exhibit similar pH profiles for a given preparation; but these concerted changes occur over different pH ranges for different preparations. Nevertheless the optical parameters are linearly correlated with the fraction of protomer for each preparation. It is concluded that the spectral properties of the dimer and the protomer are intrinsic attributes of each species and are not directly affected by changes in ambient pH.
...
PMID:Characterization of the pH-dependent dimer-to-protomer transformation of cytochrome C oxidase at alkaline pH. 4 Dec 75

Megamitochondria have been isolated from the liver of the cuprizone-fed mouse with the aid of bovine serum albumin. Phosphorylating capacities of megamitochondria, specified above, in terms of respiratory control ratios and ADP/O ratios have revealed that they are not uncoupled completely. Biochemical properties of megamitochondria which are related to the metabolism of copper have shown that copper-chelating action of cuprizone may not be directly related to the formation of megamitochondria in vivo. Namely, cytochrome contents, activities of cytochrome oxidase and monoamine oxidase and contents of copper of megamitochondria were unchanged compared with those of the control. However, contents of divalent metals such as Ca-++ and Mg-++, especially that of the former, in megamitochondria decreased significantly. It is suggested that cuprizone may alter Mg-++/Ca-++ ratios when it is administered in vivo, and that changes in the ratio might play a key role in the formation of megamitochondria.
...
PMID:Mechanism of the formation of megamitochondria induced by copper-chelating agents. II. Isolation and some properties of megamitochondria from the cuprizone-treated mouse liver. 16 53

Comparisons were made between specimens of intestinal mucosa from three young Friesian steers, killed when showing clinical signs associated with copper deficiency, and three controls that had received supplementary copper. Copper deficiency was associated with marked depletion of cytochrome oxidase in the epithelium of the duodenum, jejunum and ileum, and with partial villus atrophy in the duodenum and jejunum. Enterocytes from the duodenum, jejunum and ileum showed mitochondrial abnormalities ranging from slight swelling to marked localised dilation. Many of the mitochondria not affected by swelling had a distinctly condensed appearance. These changes are discussed in relation to the copper-responsive diarrhoea that affects a proportion of cattle suffering from copper deficiency.
...
PMID:Changes in enterocyte mitochondria associated with deficiency of copper in cattle. 16 9

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.
...
PMID:Kinetic studies on the reaction between cytochrome c oxidase and ferrocytochrome c. 16 79

1) Cells of Saccharomyces cerevisiae have been analysed by single and double-bean spectroscopy. Evidence is given for two components of cytochrome c oxidase in the alpha-region of their absorption spectrum. A rapidly reduceable component with a maximum at 600 nm and a slowly reduceable component with a maximum at 604 nm contribute about equal amounts to the total alpha-absorption of cytochrome c oxidase. 2) The component absorbing at 600 nm was identified as the high-potential component with a redox potential of 340 - 355mV, and the 604-nm component as the low-potential component of cytochrome c oxidase with redox potential of 180 - 190 mV. 3) Both components can be characterized by analysing the reduction kinetics in the presence of carbon monoxide. In the presence of saturating concentrations of carbon monoxide, an oxygen pulse leads to a rapid oxidation and subsequent reduction of cytochrome c oxidase, but the rapid reduction phase at 600 nm completely disappears, demonstrating its identity with cytochrome a3, which, being liganded by carbon monoxide in its reduced state, cannot react any more. The component which becomes oxidized and later reduced in the presence of carbon monoxide -- by definition cytochrome a -- has an absorption maximum at 604 nm. 4) The total extinction change at 604 nm in the presence of carbon monoxide is nearly as high as in its absence, but the reduction occurs in two phases and only the second phase, which contributes 50 - 60% to the total absorbance, corresponds in redox potential and kinetic properties to cytochrome a. Because the redox potential of the first reduction phase is very close to that of the low-potential copper atom of cytochrome c oxidase, it is concluded that the apparent increase in the extinction coefficient of cytochrome a in the presence of carbon monoxide is the result of a strong interaction between the ligand fields of cytochrome a and copper, induced by the binding of carbon monoxide to reduced cytochrome a3.
...
PMID:Identification of cytochrome a and a3 in yeast cells. 17 24

Flash photolysis of the membrane-bound cytochrome oxidase/carbon monoxide compound in the presence of oxygen at low temperatures and in the frozen state leads to the formation of three types of intermediates functional in electron transfer in cytochrome oxidase and reduction of oxygen by cytochrome oxidase. The first category (A) does not involve electron transfer to oxygen between -125 degrees and -105 degrees, and includes oxy compounds which are spectroscopically similar for the completely reduced oxidase (Cu1+alpha3(2+)-O2) or for the ferricyanide-pretreated oxidase (Cu2+alpha3(3+)-O2). Oxygen is readily dissociated from compounds of type A. The second category (B) involves oxidation of the heme and the copper moiety of the reduced oxidase to form a peroxy compound (Cu2+alpha 3(3+)-O2=or Cu2+alpha3(2+)-O2H2) in the temperature range from -105 degrees to -60 degrees. Above -60 degrees, compounds of type B serve as effective electron acceptors from cytochromes a, c, and c1. The third category (C) is formed above -100 degrees from mixed valency states of the oxidase obtained by ferricyanide pretreatment, and may involve higher valency states of the heme iron (Cu2+alpha3(4+)-O2=). These compounds act as electron acceptors for the respiratory chain and as functional intermediates in oxygen reduction. The remarkable features of cytochrome oxidase are its highly dissociable "oxy" compound and its extremely effective electron donor reaction which converts this rapidly to tightly bound reduced oxygen and oxidized oxidase.
...
PMID:Functional intermediates in the reaction of membrane-bound cytochrome oxidase with oxygen. 17 5


1 2 3 4 5 6 7 8 9 10 Next >>

---