Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.9.3.1 (cytochrome oxidase)
 8,822 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A cytochrome c derivative from which iron is removed has been prepared and characterized. Several lines of evidence indicate that native and porphyrin cytochrome c have similar conformations: they have similar elution characteristics on Sephadex gel chromatography; in both proteins the tryptophan fluorescence is quenched and the pK values of protonation of the porphyrin are identical. Porphyrin cytochrome c does not substitute for native cytochrome c in either the oxidase reaction or in restoring electron transport in cytochrome-c-depleted mitochondria. It does however competitively inhibit native cytochrome c in these reactions, the Ki for inhibition being larger than the Km for reaction. The absorption and emission spectra, and the polarized excitation spectrum of the porphyrin cytochrome c are characteristic of free base porphyrin. The absence of fluorescence quenching of porphyrin cytochrome c when the protein is bound to cytochrome oxidase suggests that heme to heme distance between these proteins is larger than 0.5 to 0.9 nm depending upon orientation. Binding of the porphyrin cytochrome c to phospholipids or to mitochondria increases the fluorescence polarization of a positively polarized absorption band, which indicates that the bound form of the protein does not rotate freely within the time scale of relaxation from the excited state.
 ...
PMID:Cytochrome c interaction with membranes. Absorption and emission spectra and binding characteristics of iron-free cytochrome c. 0 Dec 65

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

1. A detailed study of cytochrome c oxidase activity with Keilin-Hartree particles and purified beef heart enzyme, at low ionic strength and low cytochrome c concentrations, showed biphasic kinetics with apparent Km1 = 5 x 10(-8) M, and apparent Km2 = 0.35 to 1.0 x 10(-6) M. Direct binding studies with purified oxidase, phospholipid-containing as well as phospholiptaining aid-depleted, demonstrated two sites of interaction of cytochrome c with the enzyme, with KD1 less than or equal to 10(-7) M, and KD2 = 10(-6) M. 2. The maximal velocities as low ionic strength increased with pH and were highest above ph 7.5. 3. The presence and properties of the low apparent Km phase of the kinetics were strongly dependent on the nature and concentration of the anions in the medium. The multivalent anions, phosphate, ADP, and ATP, greatly decreased the proportion of this phase and similarly decreased the amount of high affinity cytochrome c-cytochrome oxidase complex formed. The order of effectiveness was ATP greater than ADP greater than P1 and since phosphate binds to cytochrome c more strongly than the nucleotides, it is concluded that the inhibition resulted from anion interaction with the oxidase. 4mat low concentrations bakers' yeast iso-1, bakers' yeast iso-1, horse, and Euglena cytochromes c at high concentrations all attained the same maximal velocity. The different proportions of low apparent Km phase in the kinetic patterns of these cytochromes c correlated with the amounts of high affinity complex formed with purified cytochrome c oxidase. 5. The apparent Km for cytochrome c activity in the succinate-cytochrome c reductase system of Keilin-Hartree particles was identical with that obtained with the oxidase (5 x 10(-8) M), suggesting the same site serves both reactions. 6. It is concluded that the observed kinetics result from two catalytically active sites on the cytochrome c oxidase protein of different affinities for cytochrome c. The high affinity binding of cytochrome c to the mitochondrial membrane is provided by the oxidase and at this site cytochrome c can be reduced by cytochrome c1. Physiological concentrations of ATP decrease the affinity of this binding to the point that interaction of cytochrome c with numerous mitochondrial pholpholipid sites can competitively remove cytochrome c from the oxidase. It is suggested that this effect of ATP represents a possible mechanism for the control of electron flow to the oxidase.
 ...
PMID:Correlation of the kinetics of electron transfer activity of various eukaryotic cytochromes c with binding to mitochondrial cytochrome c oxidase. 0

During the "respiratory adaptation" of Bacillus coagulans, it was possible to dissociate the kinetics of cytochrome a and a3 synthesis with carbon monoxide. The synthesis of cytochrome a3 is preferentially repressed when the pH of the incubation medium is pH 6.5 instead of pH 5.5. However, though the total synthesis of tetrapyrrole compounds is the same at both pH values, the excretion of coproporphyrin III is much increased at pH 6.5. Bacillus coagulans, sensitive to the "glucose effect", shows the "pH effect" only in the presence of high glucose concentrations. The repression of the oxidase complex synthesis by a slight increase of the extracellular pH appears directly related to the increase of the extracellular coproporphyrin III.
 ...
PMID:[Study of the mechanism of the effect of extracellular pH on the synthesis of the oxidative complex (cytochrome a+a3) of Bacillus coagulans: relationship to the "glucose effect" and role of excreted coproporphyrin III (author's transl)]. 0

1. Formate inhibits cytochrome c oxidase activity both in intact mitochondria and submitochondrial particles, and in isolated cytochrome aa3. The inhibition increases with decreasing pH, indicating that HCOOH may be the inhibitory species. 2. Formate induces a blue shift in the absorption spectrum of oxidized cytochrome aa3 (a3 + a33+) and in the half-reduced species (a2 + a33+). Comparison with cyanide-induced spectral shifts, towards the red, indicates that formate and cyanide have opposite effects on the aa3 spectrum, both in the fully oxidized and the half-reduced states. The formate spectra provide a new method of obtaining the difference spectrum of a32+ minus a33+, free of the difficulties with cyanide (which induces marked high leads to low spin spectral shifts in cytochrome a33+) and azide (which induces peak shifts of cytochrome a2+ towards the blue in both alpha- and Soret regions). 3. The rate of formate dissociation from cytochrome a2+ a33+ -HCOOH is faster than its rate of dissociation from a3+ a33+ -HCOOH, especially in the presence of cytochrome c. The Ki for formate inhibition of respiration is a function of the reduction state of the system, varying from 30 mM (100% reduction) to 1 mM (100% oxidation) at pH 7.4, 30 degrees C. 4. Succinate-cytochrome c reductase activity is also inhibited by formate, in a reaction competitive with succinate and dependent on [formate]2. 5. Formate inhibition of ascorbate plus N, N, N', N'-tetramethyl-p-phenylenediamine oxidation by intact rat liver mitochondria is partially released by uncoupler addition. Formate is permeable through the inner mitochondrial membrane and no differences in 'on' or 'off' inhibition rates were observed when intact mitochondria were compared with submitochondrial particles. 6. NADH-cytochrome c reductase activity is unaffected by formate in submitochondrial particles, but mitochondrial oxidation of glutamate plus malate is subject both to terminal inhibition at the cytochrome aa3 level and to a slow extra inhibition by formate following uncoupler addition, indicating a third site of formate action in the intact mitochondrion.
 ...
PMID:The effect of formate on cytochrome aa3 and on electron transport in the intact respiratory chain. 0 41

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.
 ...
PMID:Isolation and partial characterization of the cytochrome oxidase from Rhodopseudomonas palustris. 0 86

A microsomal fraction, prepared from mouse skin, catalyzed the hydroxylation of benzpyrene and aniline and the deethylation of 7-ethoxycoumarin. Contamination of the preparation by cytochrome oxidase and cytochrome P-420 was determined by spectral analysis. The enzyme activities studied in mouse skin (Swiss-Webster CD-1) did not respond to topical application of 3-MC. Twenty-four hours after topical application of TCDD to mice, microsomes from skin had 50% greater benzpyrene hydroxylase and 7-ethoxycoumarin deethylase activity, and 4- to 8-fold greater activity of these enzymes was seen after 72 hr. Increases in cytochrome P-450 content of skin microsomes could be demonstrated 24 and 72 hr after topical TCDD treatment of mice. Cholate treatment (solubilization) of skin microsomes, followed by centrifugation, removed the contaminating cytochrome oxidase. Quantitative and qualitative analyses of cytochrome P-450 difference spectra were made from the solubilized preparations.
 ...
PMID:Cytochrome P-450 content and mixed-function oxidase activity in microsomes isolated from mouse skin. 1 Jan 43

1. Cytochrome c2+ increases the rate at which cytochrome oxidase (EC 1.9.3.1) gamma max428nm) converts to its conformational isomer (gamma max 418-423 nm) but cytochrome c3+ has little effect on the conversion rate. 2. Interactions between reduced cytochrome oxidase and cytochrome c were studied in the absence of electron flow using anaerobic Sephadex columns. 3. Oxidase that is reduced by cytochrome c2+ or other reductant forms the 418-to 423-nm isomer if its last contact, before oxidation, is with cytochrome c3+. If the reduced oxidase contacts cytochrome c2+, before oxidation, the 428-nm oxidase forms.
 ...
PMID:The interactions between cytochrome c and cytochrome oxidase that determine the conformation of the oxidized oxidase. 1 13

Oxidized and reduced manganese cytochromes c, Mn Cyt c+ and Mn Cyt c, have been synthesized. Mn Cyt c+ and Fe Cyt c+ have identical electrophoretic and ion exchange mobilities. Mn Cyt c+ does not bind F-, CN-, or N3- ions; Mn Cyt c does not bind CO or O2. Mn Cyt c is very rapidly autooxidized by O2 even at -50 degrees. The manganese ion is readily dissociated from Mn Cyt c at acidic pH values. Both Mn Cyt c and Mn Cyt c+ are high spin complexes with 3d5 S = 5/2 and 3d4 S = 2 electronic configurations, respectively. The epr spectrum of Mn Cyt c is rhombic with (formula: see text). Both oxidized and reduced Mn Cyt c react with NO; the former reaction is reversible and the product has the following epr spectral parameters: (formula: see text). There is no superhyperfine interaction observable with the NO ligand, and the unpaired electron density is estimated to be mostly in the metal ion d xy orbital. The structure is best formulated as Mn Cyt c (NO)+. The half-reduction potential of Mn Cyt c is + 60 +/- 40 mV. It is neither oxidized by cytochrome oxidase nor reduced by NADH, NADPH, or succinate cytochrome reductase. These physical, chemical, and enzymic properties of manganese cytochromes c suggest a five-coordinate metalloporphyrin prosthetic group with the manganese ion situated significantly out-of-plane toward the side of His-18.
 ...
PMID:Manganese cytochrome c. Structure and properties. 1 68

We report 441.6 nm excitation resonance Raman spectra of oxidized and reduced monomeric heme a-imidazole, cytochrome oxidase-exogenous ligand complexes in various redox states, and alkaline denatured oxidase. These data show that, in reduced oxidase, the cytochrome a3 Raman spectrum has bands at 215, 364, 1230, and 1670 cm-1 not observed in the cytochrome a spectrum. The appearance of these bands in the reduced cytochrome a3 spectrum is due to interactions between the heme a of cytochrome a3 and its protein environment and not to intrinsic properties of heme a. These interactions are pH sensitive and strongly influence the vibrational spectra of both heme a groups. We assign the 1670-cm-1 band to the heme a formyl substituent and propose that the intensity of the 1670 cm-1 is high for reduced cytochrome a3 because the C==O lies in the porphyrin plane and is very weak for oxidized and reduced cytochrome a, oxidized cytochrome a3, and oxidized and reduced heme a-imidazole because the C==O lies out of the plane. We suggest that movement of the C==O in and out of the plane explains the ligand induced spectral shift in the optical absorption spectrum of reduced cytochrome a3. Finally, we confirm the observation of Adar & Yonetani (private communication) that, under laser illumination, resting oxidase is photoreactive.
 ...
PMID:Raman spectra of heme a, cytochrome oxidase-ligand complexes, and alkaline denatured oxidase. 2 63


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