Intermediates in the reaction of reduced cytochrome oxidase with dioxygen.
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Cytochrome c Group↗
Biomedical subjects
Y Orii
Publications and source records attributed to Y Orii.
Kinetic alterations of cytochrome c oxidase in carbon tetrachloride induced cirrhotic rat liver.
In a study of the chronic effects of CCl4 on the respiratory activities of rat liver mitochondria, the content of cytochrome c oxidase increased from 0.077 +/- 0.010 (nmol/mg protein) for normal rats to 0.101 +/- 0.009, and its specific activity increased from Vmax = 345 +/- 24 (e-/s/cytochrome aa3) to 431 +/- 19 in mitochondria of CCl4 treated rats. There was a slight increase in Km for cytochrome c from 5.63 +/- 0.08 microM to 7.79 +/- 0.80. These results would strongly suggest that an appreciable decrease in the steady state concentration of ATP in hepatic cells of CCl4 treated rats brought about a compensatory increase in the overall activity of cytochrome c oxidase. However, when the rate of oxygen uptake by mitochondria was measured in the presence of rotenone and tetramethyl-p-phenylene-diamine with NADH as substrate, the specific activity in CCl4 treated rats was lower than that of normal rats (Vmax = 345 +/- 31 (e-/s/cytochrome aa3), as compared to Vmax = 408 +/- 21) in spite of the increased activity of cytochrome c oxidase. This phenomenon was ascribed to a decrease in the activity of NADH cytochrome b5 reductase in the mitochondrial outer membrane due to CCl4 treatment.
Adenosine Triphosphate↗
A mechanism of respiratory control: studies with proteoliposomes containing cytochrome oxidase and bacteriorhodopsin.
Both beef heart cytochrome oxidase and bacteriorhodopsin of Halobacterium halobium were reconstituted into liposomes by the sonication-cholate dialysis method. The proteoliposomes showed the respiratory control ratio of 4.2, and steady-state illumination of the vesicles lead to the 2.7-fold stimulation of the oxidase activity in the absence of uncouplers. The light-stimulated state 4 respiration increased with light intensity, but light had no effect on the oxidase activity that had been relieved by addition of uncouplers. Proteoliposomes with the photosensitive oxidase activity were also obtained when cytochrome oxidase vesicles were fused with bacteriorhodopsin vesicles in the presence of calcium chloride, and the extent of photoactivation was maximally 1.4-fold. The light-induced respiratory release was observed even in the presence of valinomycin or nigericin, indicating that the oxidase activity was sensitive to both the membrane potential and the pH gradient. We propose as a mechanism of the respiratory control that the process of proton transport to the reaction center for water formation is the rate limiting step for the cytochrome oxidase activity.
Bacteriorhodopsins↗
[Reduction of molecular oxygen and proton translocation catalyzed by cytochrome oxidase].
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Electron Transport Complex IV↗
Proton translocation by cytochrome oxidase vesicles catalyzing the peroxidatic oxidation of ferrocytochrome c.
Coupled with the peroxidatic oxidation of ferrocytochrome c under anaerobic conditions, proteoliposomes reconstituted with a purified preparation of bovine heart cytochrome oxidase ejected protons into the external medium with an apparent H+/e- ratio of 0.9. At the same time, protons in the intravesicular space were consumed. Dicyclohexylcarbodiimide significantly inhibited the proton translocation. Cyanide (0.14 mM) completely inhibited both the peroxidase and proton translocating activities. On the contrary, in the presence of 1 mM CO the proton ejection was abolished almost completely, but 50% of the peroxidase activity persisted. This result suggests the operation of multiple mechanisms in the peroxidase reaction and that the CO-sensitive one is coupled to the proton translocation.
Animals↗
Photodissociation of oxygenated cytochrome o(s) (Vitreoscilla) and kinetic studies of reassociation.
Oxygenated cytochrome o(s) from Vitreoscilla was photodissociated by a laser flash but the quantum yield was low. The rebinding of oxygen to the ferrous cytochrome proceeded monophasically, and the second order rate constant was 7.8 X 10(7) M-1 s-1, the off rate constant 5.6 X 10(3) s-1, and the calculated dissociation constant for the oxygenated compound 7.2 X 10(-5) M at pH 7.3 and 25 degrees C. Rapid scanning spectroscopy revealed the formation of chytochrome o-O2 directly from ferrous chytochrome o and oxygen without any evidence for an intermediary formation of Compound D, another type of oxygenated chytochrome o. Photodissociation in solution containing CO/O2 mixtures resulted in rapid binding of oxygen followed by slow replacement by CO. This property as well as the photodissociability of chytochrome o-O2 suggests that the heme iron of the compound is in the ferrous state. In addition, the primary oxygen compound was fairly stable and did not decay further in the absence of CO, in marked contrast with that of mammalian cytochrome oxidase primary oxygen compound which rapidly decayed. This result suggests a possible role of this cytochrome as an oxygen carrier or storage.
Carbon Monoxide↗
Cytochrome c peroxidase activity of bovine heart cytochrome oxidase incorporated in liposomes and generation of membrane potential.
Cytochrome oxidase vesicles catalyzed the peroxidatic oxidation of ferrocytochrome c. The maximal peroxidase activity in the absence of an uncoupling agent was 9.8 mol ferrocytochrome c oxidized/(s X mol heme a), indicating a 5-fold activation compared with the soluble enzyme system. The peroxidase activity was further enhanced 1.2 to 2.1 times upon addition of an uncoupler, carbonyl cyanide p-trifluoromethoxyphenyl hydrazone. The stoichiometry of the reduction of hydrogen peroxide by ferrocytochrome c was established to be 1 : 2, indicating water formation. Potassium cyanide (0.14 mM) completely inhibited the peroxidase activity. The inhibition by 1 mM CO was 40-77% depending on the energized state of cytochrome oxidase vesicles, but in contrast, 85% inhibition was observed with the soluble enzyme. In the energized state the enzyme showed a slightly lower affinity for CO than in the deenergized state. Coupled with the peroxidase activity, a membrane potential of 72 mV was registered transiently; this may be physiologically significant in relation to the energy transduction mechanism.
Animals↗
Biphasic recombination of photodissociated CO compound of cytochrome o(s) from Vitreoscilla.
The soluble cytochrome o from Vitreoscilla contains two identical subunits and two hemes. The reduced form binds 2 mol of CO in a cooperative manner with a Hill coefficient near 2 (Tyree, B., and Webster, D. A. (1978) J. Biol. Chem. 253, 6988-6991). This carbonyl compound was photolysed with a dye laser and recombination followed at 437 or 420 nm where maximal absorbance changes were registered. Recombination kinetics were biphasic, and the fast phase was approximately 10 times the rate of the slow phase. Apparent rate constants of both phases showed a nonlinear dependence on CO concentration, respectively, in conformity with a reaction scheme which assumes the transient formation of an intermediate species in both slow and fast reactions. A study of temperature dependence of the reactions gave EA = 2.7 kcal/mol for the slow reaction and EA = 3.2 kcal/mol for the fast reaction below 23 degrees C; above this temperature the slope of the Arrhenius plot for the fast reaction became positive. Maximal rates for both phases were around pH 6.5 and fell to approximately 40% of maximal at pH 12. The binding reaction was affected by even a low concentration of sodium dodecyl sulfate (0.0025%), which changed both the kinetic constant of each phase and the relative contribution of each phase to the reaction. A model which assumes the existence of fast and slow reaction conformers in equilibrium is proposed.
Carbon Monoxide↗
The reaction of horseradish peroxidase with hydroperoxides derived from Triton X-100.
All of the commercially available Triton X-100 examined gave Compound I upon reaction with horseradish peroxidase, followed by its gradual transition into Compound II. Titration of horseradish peroxidase with Triton X-100 to form Compound I indicated that 1% (v/v) aqueous solutions of the detergent contained 0.4 to 3.2 microM equivalent peroxide but iodometric titration revealed 1.1 to 5.0 microM peroxide, suggesting the occurrence of different types of peroxides, reactive and unreactive with the peroxidase. The rate constant for Compound I formation was 1.5 X 10(7) M-1 S-1 at pH 7.4 at 25 degrees C, and for conversion into Compound II apparent first-order rate constants were 5.2 X 10(-3) to 1.7 X 10(-2) S-1. These results indicate that the Triton peroxides are as highly reactive as hydrogen peroxide. The amount of Triton peroxides increased as aqueous solutions of the detergent were allowed to stand, but the peroxides were destroyed by treatment with sodium borohydride. Although freshly prepared aqueous solutions of sodium cholate, sodium dodecyl sulfate, Tween 20 (polyoxyethylene sorbitan monolaurate), and Emasol 1130 (an equivalent of Tween 20) did not contain any detectable amount of peroxide, aged solutions of sodium dodecyl sulfate and Emasol 1130 contained peroxides. These observations suggest the need for appropriate precautions when biologically active substances vulnerable to attack by peroxides are incubated with Triton X-100 either for their solubilization from biomembranes or for other processing.
Chemical Phenomena↗
Formation and decay of the primary oxygen compound of cytochrome oxidase at room temperature as observed by stopped flow, laser flash photolysis and rapid scanning.
Rapid kinetic and scanning techniques were employed to observe the reaction of dioxygen with fully reduced cytochrome oxidase at room temperature following stopped flow flash photolysis of the CO compound of the enzyme. The initial product of the reaction was an oxygen compound with a spectral profile quite similar to that of the cytochrome oxidase-CO compound. The second order rate constant for formation of the primary oxygen compound was 1.1 X 10(8) M-1 S-1 at pH 7.4 and 25 degrees C. With an off rate constant of 1.9 X 10(3) S-1, the calculated dissociation constant was 1.8 X 10(-5) M. The apparent activation energy was 16.7 kJ/mol. The primary oxygen compound underwent further reaction which was independent of oxygen concentration with a rate constant of 1.2 X 10(3) S-1, and the product was Intermediate III ( Orii , Y. (1982) in Oxygenases and Oxygen Metabolism ( Nozaki , M., Yamamoto, S., Ishimura , Y., Coon , M. J., Ernster , L., and Estabrook , R., eds) pp. 137-149, Academic Press, New York), an oxidized species presumably identical to the "oxygen pulsed" oxidase. Thus, this reaction was ascribed to intramolecular electron transfer to the oxygen in the compound. The energy of activation was 49.8 kJ/mol below 18 degrees C but above that the rate constant was independent of temperature, and a "tunneling" mechanism was suggested for the intramolecular electron transfer.
Animals↗
Carbon monoxide-binding cytochromes in the respiratory chain of the thermophilic bacterium PS3 grown with sufficient or limited aeration.
The effects of aeration on the growth and cytochrome patterns of thermophilic bacterium PS3 were studied; bacteria grown with strong aeration synthesized cytochromes c, b, and aa3, while those grown with low aeration, showing non-exponential growth, synthesized higher amounts of cytochromes c and b including o, and a lower amount of cytochrome a (a3). The CO-difference spectra indicated that the terminal oxidase was cytochrome aa3 for high aeration conditions and the cytochrome o for low aeration conditions. Cytochrome o can be solubilized by Triton X-100 from the membrane fraction of bacteria grown under oxygen-limited conditions. The carbon monoxide complex of cytochrome o, obtained by exposing this extract to CO, was photolyzed and the subsequent rebinding of CO was analyzed; it followed first order kinetics with a rate constant of around 8 s-1 at 25 degrees C. At liquid nitrogen temperature, CO-rebinding did not occur. The CO-difference spectrum of purified cytochrome oxidase sample from the bacteria grown with strong aeration (Sone, N., et al. (1979) FEBS Lett. 106, 39-42) revealed the presence of a small amount of a cytochrome o-like pigment besides cytochrome aa3. Analysis of the CO complexes of these chromophores showed rate constants of 29-30 s-1 for cytochrome aa3 and 35-42 s-1 for the o-like pigment, indicating that the cytochrome o-like pigment contaminating the purified cytochrome oxidase preparation was not typical cytochrome o.
Aerobiosis↗
The cytochrome c peroxidase activity of cytochrome oxidase.
I have found that mammalian cytochrome oxidase catalyzes the peroxidatic oxidation of ferrocytochrome c under strictly anaerobic conditions. An apparent Km value for ferrocytochrome c was 2 microM, and a second order rate constant, estimated as an extrapolated value, was 1.4 X 10(6) M-1 s-1 at pH 7.4 at 25 degrees C. These values were quite similar to the corresponding values of 6.4 microM and 1.9 X 10(6) M-1 s-1 determined for the intrinsic oxidase activity. The rate of the peroxidatic oxidation showed a hyperbolic dependence on the concentration of hydrogen peroxide, and the apparent Km value ws 0.18 mM. Cyanide and azide at 0.1 mM inhibited the peroxidase activity by 100 and 98%, respectively, whereas, under carbon monoxide at 750 mm Hg, 10% of the activity still remained. Under air, cytochrome oxidase acted simultaneously as oxidase and peroxidase.
Animals↗
Evidence of increased synthesis of delta-aminolevulinic acid dehydratase in experimental lead-poisoned rats.
delta-Aminolevulinic acid dehydratase (porphobilinogen synthase; 5-aminolevulinate hydro-lyase, EC 4.2.1.24) was purified from rat and rabbit erythrocytes to a homogeneous state. Specific activities were 26.0 and 26.6 units/mg protein for the rat and rabbit enzymes, respectively, and their estimated molecular weight was 280000, each consisting of 8 subunits of Mr 35000. In order to quantitate rat delta-aminolevulinic acid dehydratase at several stages of lead-poisoning, a radioimmunoassay technique using goat antiserum against the rat enzyme was developed for the first time. This technique was specific, reproducible and highly sensitive allowing determination of ng enzyme. When drinking water containing 25 mM lead acetate was given daily to rats ad lib. the delta-aminolevulinic acid dehydratase activity in the blood, assayed without any pretreatment, decreased to 8% of the control level on the next day. On the contrary, the restored enzyme activity, assayed in the presence of Zn2+ and dithiothreitol, was greater than normal by the fourth day of lead administration in bone-marrow cells and by the ninth day in the peripheral blood. The increased activity level stayed the same from the ninth day onward. The enzyme content as determined directly by the radioimmunoassay technique at this stage was about 2-fold above that the control. There was no significant difference in the number of reticulocytes and the distribution profile of different types of reticulocytes between the lead-exposed and non-exposed rats. Therefore, the increase in the amount of delta-aminolevulinic acid dehydratase in erythrocytes of lead-poisoned rats was suggested to be due to an increased rate of synthesis in the bone-marrow cells.
Animals↗
The effect of cytochrome oxidase on lipid chain dynamics. A nanosecond fluorescence depolarization study.
Molecular motions in membranes composed of purified cytochrome oxidase (EC 1.9.3.1) and synthetic lipid (L-alpha-dimyristoylphosphatidylcholine or L-alpha-dioleoylphosphatidylcholine) at various ratios were investigated with a lipophilic fluorescent probe 1,6-diphenyl-1,3,5-hexatriene. Nanosecond fluorescence depolarization kinetics of the probe showed that the rod-shaped probe molecules perform a fast wobbling motion (restricted rotation) in all membranes studied, presumably reflecting the motion of lipid acyl chains. At temperatures where the pure lipid was in the liquid-crystalline phase, presence of cytochrome oxidase reduced the angular range of the wobbling motion, whereas its rate, the wobbling diffusion constant, was unaffected. On the other hand, incorporation of the protein into lipid in the gel phase resulted in the increase in the wobbling diffusion constant while the range of the wobbling motion remained the same. A time-dependent view of lipid dynamics that accounts for the above findings, as well as the results of recent electron spin resonance and nuclear spin resonance studies of protein-lipid interactions, is proposed.
Animals↗
Nanosecond time-resolved fluorescence investigations of temperature-induced conformational changes in cytochrome oxidase in phosphatidylcholine vesicles and solubilized systems.
Intrinsic and lipid phase transition-induced conformational changes in cytochrome oxidase in phosphatidylcholine vesicle and solubilized systems were examined by the fluorescence lifetime of N-(1-anilinonaphthyl-4)-maleimide conjugated with the enzyme. The time-dependent fluorescence intensity of N-(1-anilinonaphthyl-4)-maleimide attached to cytochrome oxidase was described as a triple exponential decay. Both the intrinsic and lipid phase transition-induced conformational changes were detectable in plots of the average lifetime against temperature. In most cases a peak occurred at the temperature of the conformational change. The time-dependent emission anisotropy showed that N-(1-anilinonaphthyl-4)-maleimide embedded in cytochrome oxidase in phosphatidylcholine vesicles underwent a rapid restricted wobbling within a cone. The half-angle of the cone was around 30 degrees for cytochrome oxidase in dimyristoyl phosphatidylcholine vesicles.
Animals↗
Fluorescent probe study of temperature-induced conformational changes in cytochrome oxidase in lecithin vesicle and solubilized systems.
A protein-bound label, N-(1-anilinonaphthyl-4)-maleimide (ANM), was used to investigate conformational changes in bovine heart cytochrome oxidase. The fluidity of cytochrome oxidase vesicles was monitored by a lipophilic probe, 1,6-diphenyl-1,3,5-hexatriene. The fluroescence intensity and emission anisotropy of these probes were examined between 4 and 60 degrees C in enzyme--dipalmitoyllecithin vesicles, in enzyme--dimyristoyllecithin vesicles, in enzyme--dioleoyllecithin vesicles, and in the soluble enzyme. The temperature-dependent changes in these quantities indicated that there were two types of conformational changes in oxidized cytochrome oxidase: one was attributed to an intrinsic enzyme conformation change which occurred around 20 degrees C, and the other was attributed to a conformational change induced by the lipid phase transition. Although ANM-reactive subunits of cytochrome oxidase in these four lecithin vesicle and solubilized systems were different from each other, subunit I always reacted with ANM in preference to other subunits.
Animals↗
Photodissociation of cytochrome oxidase-nitric oxide at low temperatures.
Spectrophotometric studies revealed the irreversible photodissociation of reduced cytochrome oxidase-nitric oxide (NO) at 5 K. The dissociated NO recombined as the sample temperature was raised, and the half-recombination temperature was 65 K. The photodissociation at 5K was also confirmed by a change in the EPR spectrum; that is, ferroheme a-NO signals at gx=2.09 and gm=2.006 were replaced by a new signal at gm=2.03, and this change was reversed at the temperature of liquid nitrogen. Comparison of such behavior with that of cytochrome oxidase-carbon monoxide led us to propose that on photodissociation of NO from heme iron, the NO was trapped specifically at a site near the heme iron producing a new paramagnetic species. Its identification will require further studies.
Animals↗