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. The results of non-linear optimization studies on the mechanism of reaction of solid-state fully reduced membrane-bound cytochrome oxidase with CO over the 178--203 K range are presented. The analysis is carried out on data obtained by dual-wavelength multichannel spectroscopy at three wavelength pairs (444--463 nm, 590--630 nm and 608--630 nm), which yield three distinct progress curves. The only model that satisfies the triple requirement of a standard deviation within the standard error of the data, a random distribution of residuals and good determination of the optimized parameters is a two-species sequential mechanism: flash photolysis yields unliganded cytochrome oxidase and free CO, which then recombine to form species Ic; Ic is then converted into species IIc, which is identical with the cytochrome oxidase-CO complex existing before flash photolysis. All the thermodynamic parameters describing this model are calculated. 2. On the basis of the data obtained from this paper, together with data from potentiometric studies, magnetic susceptibility measurements and i.r. spectroscopy, the chemical identity of the species is suggested.
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PMID:The kinetics and thermodynamics of the reaction of solid-state fully reduced membrane-bound cytochrome oxidase with carbon monoxide as studied by dual-wavelength multichannel spectroscopy and flash photolysis. 21 48

The existence of a temperature-induced absorption band centred in the region of 666 nm is demonstrated for both membrane-bound and soluble cytochrome oxidase in the frozen state. The 666 nm band is generated solely by an increase in temperature of both fully reduced and mixed valence state cytochrome oxidase in the presence of CO or O2 within the 'pocket' containing the active site; it is not formed in the absence of both CO and O2 from the sample. The formation of the 666 nm band is entirely reversible when the temperature is decreased again and its formation is not dependent on the presence of liganded CO at the sixth coordination site of haem a3 in the low temperature range (below --120 degrees C) prior to photolysis. The shape and intensity of the 666 nm band are not affected by the extent of CO recombination following flash and photolysis and temperature increase and are not affected by changes in the valence states of the four metal centres when the O2 reaction is in progress.
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PMID:A temperature-induced absorption band centered in the region of 666 nm related to the configuration of the active site in frozen cytochrome oxidase. 21 27

The kinetics of the reaction of fully reduced membrane-bound cytochrome oxidase with O2 obtained in the Soret, alpha and near-i.r. regions were analysed, and the contributions of the three intermediates of the reaction [Clore & Chance (1978) Biochem. J. 173, 799--810] to seven wavelength pairs (430--463, 444--463, 590--630, 608--630, 740--940, 790--940 and 830--940 nm) were determined. The nature of the intermediates is discussed on the basis of the data in the present paper together with data in the literature from optical wavelength scanning, e.p.r., i.r. and magnetic-susceptibility studies.
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PMID:Low-temperature kinetics of the reactions of fully reduced membrane-bound cytochrome oxidase with oxygen in the Soret, alpha and near-infrared regions. 21 47

Compound C2 is a product of the reaction of O2 and the mixed-valence state of cytochrome oxidase. The mixed-valence state of membrane-bound cytochrome oxidase is obtained at -24 degrees C, by using either ferricyanide or yeast peroxidase complex ES as oxidants, and the configurations of oxidized haem a and its associated copper (a3+Cua2+) and of reduced haem a3 and its associated copper (ac3+.CO.Cua3+) are obtained. The mixed-valence-state cytochrome oxidase mixed with O2 at -24 degrees C and flash-photolysed at -60 to -100 degrees C reacts with O2 and initially forms an oxy compound (A2) similar to that formed from the fully reduced state (A1). Thereafter the course of the reaction differs from that obtained in the fully reduced state, and absorbance increases are observed at 740--750 nm and 609 nm and a decrease at 444 nm, with no increase in absorbance at 655 nm. One possible attribution of the absorbance increases is to charge-transfer interaction between the iron of haem a3 and the copper associated with haem a3, Cua3(2+), having properties of a type-I 'blue' copper. A possible attribution of the decrease in absorbance at 444 nm is to liganding of a3(2+). A related explanation is that the 609 nm absorbance involves a charge-transfer interaction of both iron and copper as a mixed-valence binuclear complex, Cua3, having properties of a non-blue copper. Intermediates in addition to Compound C2 are not yet identifiable by chemical or spectroscopic tests. The kinetic and equilibrium properties of Compound C2 are described.
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PMID:Compound C2, a product of the reaction of oxygen and the mixed-valence state of cytochrome oxidase. Optical evidence for a type-I copper. 22 Sep 56

The site of Na+-dependent activation in the respiratory chain of the marine bacterium, Vibrio alginolyticus, was investigated. The respiratory chain system contained ubiquinones (Q), menaquinones (MK), cytochromes b(560), c(553), d(630), and o(560). The membrane-bound and partially purified NADH dehydrogenase was stimulated 2- to 3-fold by the addition of 0.2 M Na+ or K+ and no specific requirement for Na+ was observed in this reaction step. The cytochrome oxidase showed no requirement for monovalent cations. The respiratory activity (NADH oxidase) of the membrane was lost on removal of the quinones, and the reincorporation of authentic Q-10 or MK-4 restored the activity. The rate of MK-4 reduction by NADH (menaquinone reductase) as measured using MK-4 incorporated membrane was activated by Na+, but only slightly by K+. The apparent Ka for Na+ was 78 mM for both menaguinone reductase and NADH oxidase. The requirement for Na+ of menaquinone reductase was greatly reduced in the presence of 0.2 M K+. Ubiquinone reductase as measured by using Q-10 incorporated membrane was also activated more effectively by Na+ than by K+. These results strongly suggested that the site of Na+-dependent activation in the respiratory chain of marine V. alginolyticus was at the step of NADH; quinone oxidoreductase.
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PMID:NADH: quinone oxidoreductase as a site of Na+-dependent activation in the respiratory chain of marine Vibrio alginolyticus. 45 42

The three-subunit aa3-type cytochrome c oxidase (EC 1.9.3.1) of Rhodobacter sphaeroides is structurally and functionally homologous to the more complex mitochondrial oxidase. The largest subunit, subunit I, is highly conserved and predicted to contain 12 transmembrane segments that provide all the ligands for three of the four metal centers: heme a, heme a3, and CuB. A variety of spectroscopic techniques identify these ligands as histidines. We have used site-directed mutagenesis to change all the conserved histidines within subunit I of cytochrome c oxidase from Rb. sphaeroides. Analysis of the membrane-bound and purified mutant proteins by optical absorption and resonance Raman spectroscopy indicates that His-102 and His-421 are the ligands of heme a, while His-284, His-333, His-334, and His-419 ligate the heme a3-CuB center. To satisfy this ligation assignment, helices II, VI, VII, and X, which contain these histidine residues, must be in close proximity. These data provide empirical evidence regarding the three-dimensional protein structure at the catalytic core of cytochrome c oxidase.
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PMID:Definition of the catalytic site of cytochrome c oxidase: specific ligands of heme a and the heme a3-CuB center. 131 71

The cupredoxin fold, a Greek key beta-barrel, is a common structural motif in a family of small blue copper proteins and a subdomain in many multicopper oxidases. Here we show that a cupredoxin domain is present in subunit II of cytochrome c and quinol oxidase complexes. In the former complex this subunit is thought to bind a copper centre called CuA which is missing from the latter complex. We have expressed the C-terminal fragment of the membrane-bound CyoA subunit of the Escherichia coli cytochrome o quinol oxidase as a water-soluble protein. Two mutants have been designed into the CyoA fragment. The optical spectrum shows that one mutant is similar to blue copper proteins. The second mutant has an optical spectrum and redox potential like the purple copper site in nitrous oxide reductase (N2OR). This site is closely related to CuA, which is the copper centre typical of cytochrome c oxidase. The electron paramagnetic resonance (EPR) spectra of both this mutant and the entire cytochrome o complex, into which the CuA site has been introduced, are similar to the EPR spectra of the native CuA site in cytochrome oxidase. These results give the first experimental evidence that CuA is bound to the subunit II of cytochrome c oxidase and open a new way to study this peculiar copper site.
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PMID:Restoration of a lost metal-binding site: construction of two different copper sites into a subunit of the E. coli cytochrome o quinol oxidase complex. 132 68

Brochothrix thermosphacta, grown in batch culture in a yeast-dextrose broth, at temperatures from 30 degrees C to 10 degrees C, contained diverse membrane-bound respiratory cytochromes. Under conditions of moderate aeration, cytochromes of the a-, b- and d-type were detected at all growth temperatures, but the proportions changed as a function of temperature, with the spectra of cells grown at 10 or 15 degrees C being dominated by a-type cytochrome(s). Cytochrome a3 was detected by its reactions with CO and cyanide in cells from all growth conditions. An additional cytochrome a, which was not cyanide-reactive, was also detected, suggesting the presence of an aa3 oxidase complex. Cytochrome d was cyanide- and CO-reactive, but not detectable in photodissociation spectra, presumably because of the very rapid recombination of CO at the sub-zero temperatures used. Decreasing the oxygen transfer rates to batch cultures resulted in enhanced expression of cytochrome d and changed the proportion of the aa3-type oxidase that could be attributed to ligand-binding cytochrome a3; at the lowest oxygen transfer rates, no cytochrome a was detected, suggesting the presence of a cytochrome ba3 terminal oxidase complex. Intact cells showed no evidence of a c-type cytochrome and no haem C was detected in membrane preparations. After growth at 10 degrees C, the cytochrome composition of B. campestris was essentially identical to that of B. thermosphacta. The multiplicity of putative terminal oxidases in B. thermosphacta is discussed.
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PMID:The cytochrome composition of the meat spoilage bacterium Brochothrix thermosphacta: identification of cytochrome a3-and d-type terminal oxidases under various conditions. 133 39

A strategy for the immobilization of cytochrome-c oxidase, used as a representative membrane-bound enzyme, into so-called magnetoliposomes has been developed. The latter structures consist of a phospholipid bilayer which covers nanometer-sized Fe3O4 colloids. Incorporation of the enzyme into the phospholipid envelope is facilitated by a short sonication step. Upon adsorption, the reaction characteristics of the lipid-depleted enzyme are drastically changed. With double-layered phosphatidylcholine (PC) magnetoliposomes the activity increases by a factor of approximately 5. After a first magnetic fractionation step, approximately 67% of the activity remains with the magnetoliposome retentate. Subsequent magnetophoresis cycles show that the adsorbed enzyme is firmly fixed into the phospholipid coat. Upon immobilization, the thermal behavior is also profoundly affected. The heating inactivation curves show two sigmoidal transition zones. Irrespective of the PC type used, a first inflection point is located near 39 degrees C, whereas a second one, which is located at higher temperatures, clearly depends on the acyl chain length (56 degrees C with dimyristoyl-PC and 60 degrees C for dioleoyl-PC and Ovothin-200). An identical behavior is observed with classical proteoliposomes with an equal phospholipid composition. By contrast, monolayer-coated dimyristoyl-PC magnetic structures are inferior with respect to both their reactivation potency and their ability to strongly affix cytochrome-c oxidase and to improve the thermal stability of the enzyme.
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PMID:Binding characteristics and thermal behaviour of cytochrome-C oxidase, inserted into phospholipid-coated, magnetic nanoparticles. 133 72

A complete pathway for Azorhizobium caulinodans nicotinate catabolism has been determined from mutant phenotype analyses, isolation of metabolic intermediates, and structural studies. Nicotinate serves as a respiratory electron donor to O2 via a membrane-bound hydroxylase and a specific c-type cytochrome oxidase. The resulting oxidized product, 6-hydroxynicotinate, is next reduced to 1,4,5,6-tetrahydro-6-oxonicotinate. Hydrolytic ring breakage follows, with release of pyridine N as ammonium. Decarboxylation then releases the nicotinate C-7 carboxyl group as CO2, and the remaining C skeleton is then oxidized to yield glutarate. Transthioesterification with succinyl coenzyme A (succinyl-CoA) yields glutaryl-CoA, which is then oxidatively decarboxylated to yield crotonyl-CoA. As with general acyl beta oxidation, L-beta-hydroxybutyryl-CoA, acetoacetyl-CoA, and finally two molecules of acetyl-CoA are produced. In sum, nicotinate is catabolized to yield two CO2 molecules, two acetyl-CoA molecules, and ammonium. Nicotinate catabolism stimulates Azorhizobium N2 fixation rates in culture. Nicotinate catabolism mutants still able to liberate pyridine N as ammonium retain this capability, whereas mutants so blocked do not. From, mutant analyses and additional physiological tests, N2 fixation stimulation is indirect. In N-limited culture, nicotinate catabolism augments anabolic N pools and, as a consequence, yields N2-fixing cells with higher dinitrogenase content.
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PMID:Elucidation of the complete Azorhizobium nicotinate catabolism pathway. 144 45


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