共查询到20条相似文献,搜索用时 31 毫秒
1.
L R deAlvare K Goda T Kimura 《Biochemical and biophysical research communications》1976,69(3):687-694
The mechanism of the reaction of bis-(salicylato)-copper(II) with superoxide anion has been studied by utilizing electron paramagnetic resonance and polarographic techniques. The proposed reaction sequence is as follows: Using the xanthine-xanthine oxidase system as a superoxide generator, it was found that the concentration of this copper complex for 50% inhibition of the xanthine-cytochrome c reductase activity was about 1000 times more per mole of copper than that of erythrocyte superoxide dismutase. 相似文献
2.
In order to test the question if a pool of lipophilic ions may exist in black lipid membranes which cannot be detected by electrical relaxation measurements we have performed simultaneously measurements of the optical absorption of a lipophilic ion. The absorbance of membrane-bound dipicrylamine at 410 nm was measured with a sensitive spectrophotometer which can detect absorbance changes . A minimal concentration of about 6 · 1011 dipicrylamine ions per cm2 of the membrane could be detected with this instrument. The dipicrylamine concentration in the membrane obtained with the optical method is compared with the concentrations obtained from simultaneous electrical relaxation measurements. and agreed at low dipicrylamine concentrations (10?8–10?7 M in the aqueous phase) and showed saturation at higher concentrations (up to 5 · 10?6 M). In the saturation range was maximally four times higher than . The significance of this difference is discussed together with general aspects of the saturation phenomenon. 相似文献
3.
(1) +/electron acceptor ratios have been determined with the oxidant pulse method for cells of denitrifying Paracoccus denitrificans oxidizing endogenous substrates during reduction of O2, NO?2 or N2O. Under optimal H+-translocation conditions, the ratios , , for reduction to N2 and for reduction to N2O were 6.0–6.3, 4.02, 5.79 and 3.37, respectively. (2) With ascorbate/N,N,N′,N′-tetramethyl-p-phenylenediamine as exogenous substrate, addition of NO?2 or N2O to an anaerobic cell suspension resulted in rapid alkalinization of the outer bulk medium. , for reduction to N2 and for reduction to N2O were ?0.84, ?2.33 and ?1.90, respectively. (3) The ratios, mentioned in item 2, were not altered in the presence of and the triphenylmethylphosphonium cation. (4) A simplified scheme of electron transport to O2, NO?2 and N2O is presented which shows a periplasmic orientation of the nitrite reductase as well as the nitrous oxide reductase. Electrons destined for NO?2, N2O or O2 pass two H+-translocating sites. The acceptor ratios predicted by this scheme are in good agreement with the experimental values. 相似文献
4.
Raili Myllylä Lutz M. Schubotz Ulrich Weser Kari I. Kivirikko 《Biochemical and biophysical research communications》1979,89(1):98-102
Four superoxide dismutase active copper chelates, Cu(acetylsalicylate)2, Cu(salicylate)2, Cu(lysine)2 and Cu(tyrosine)2, proved to be inhibitors of prolyl and lysyl hydroxylase. The kinetics of the inhibition are consistent with the proposal that these compounds dismutated at the active site of the enzymes. The data strongly suggest that is the active form of O2 in the prolyl and lysyl hydroxylase reactions. 相似文献
5.
ADP and Pi-loaded membrane vesicles from l-malate-grown Bacillus alcalophilus synthesized ATP upon energization with . ATP synthesis occurred over a range of external pH from 6.0 to 11.0, under conditions in which the total protonmotive force was as low as ?30 mV. The phosphate potentials (ΔGp) were calculated to be 11 and 12 kcal/mol at pH 10.5 and 9.0, respectively, whereas the values in vesicles at these two pH values were quite different (?40 ± 20 mV at pH 10.5 and ?125 ± 20 mV at pH 9.0). ATP synthesis was inhibited by KCN, gramicidin, and by N,N′-dicyclohexylcarbodiimide. Inward translocation of protons, concomitant with ATP synthesis, was demonstrated using direct pH monitoring and fluorescence methods. No dependence upon the presence of Na+ or K+ was found. Thus, ATP synthesis in B. alcalophilus appears to involve a proton-translocating ATPase which functions at low . 相似文献
6.
K G Brown W L Peticolas E Brown 《Biochemical and biophysical research communications》1973,54(1):358-364
Laser Raman spectra of concentrated samples of phosphatidyl choline and phosphatidyl ethanolamine were taken at approximately 10° intervals over a temperature range of 90°–19°C. The spectral region from 30 to 3300 cm?1 was investigated. Several new spectral features were discovered which are correlated to phospholipid liquid crystalline structure. It is shown that 1) frequency shifts occur in the symmetric stretch band which suggest a change in exposure of the PO2 group to the solvent upon melting, 2) the frequency of the translational hydrocarbon mode around 150 cm?1 appears to indicate the degree to which the hydrocarbon chain is extended, 3) the methyl and methylene stretch bands at 2890 and 2850 cm?1 very clearly demonstrate hydrocarbon chain melting, and 4) the 720 cm?1 band, previously assigned to the symmetric OPO diester stretch, appears to be due instead to the symmetric CN stretch of choline. 相似文献
7.
The distribution of activity was studied in cell fractions prepared from homogenates of rat liver. The level of mitochondrial contamination in the microsomal fraction depended on the fractionation procedure and on the method of homogenization. With proper care, microsomes with undetectable mitochondrial contamination could be prepared. These microsomes had no detectable activity. Approximately 85 % of the total activity of the post 6000 x g · min supernatant was recovered in the mitochondrialfraction. The properties of this mitochondrial were not distinguishable from those of the various microsomal previously described by other investigators. 相似文献
8.
The rate-determining step of the cysteine-catalyzed deiodination of 5-iodouracil is the formation of 5-iodo-6-cysteinyl-5,6-dihydrouracil. The rate of the reaction depends upon the concentration of un-ionized 5-iodouracil and the following ionic species of cysteine; ?OOC(NH3+)CHCH2S?. Unlike the reaction of 2-mercapto-ethanol with 5-iodouracil, the cysteine reaction is not subject to catalysis by imidazolium ion and tris(hydroxymethyl)aminomethane hydrochloride. When the rates of cysteine reacting with 5-iodouracil are measured in both H2O and D2O, a large kinetic isotope effect is observed (), thus implicating the protonated α amino group of cysteine as an intramolecular general acid catalyst for the reaction. These results and possible mechanisms for the actual dehalogenation of the intermediate 5-iodo-6-cysteinyl-5,6-dihydrouracil are discussed in terms of a possible mechanism for enzymatic halopyrimidine dehalogenation. 相似文献
9.
G W Ruddock J A Raleigh C L Greenstock 《Biochemical and biophysical research communications》1981,102(1):554-560
A steady-state competition system has been developed to investigate the reactions of the superoxide radical anion () with various peroxides, including the so-called Haber-Weiss reaction. Potassium superoxide dissolved in an oxygen-free solution of DMSO containing 18-dicyclohexyl-6-crown, is the source of . High pressure liquid chromatography is used as an assay system for reactivity, to detect and quantitate the yield of anthracene, formed as a major product in the reaction between and 9,10-dihydroanthrancene. Decrease in anthracene yields, in the presence of peroxide, may be used to indicate a possible competing reaction between and added peroxide. Complications involving peroxide-stimulated formation of anthraquinone derivatives are discussed. No evidence for a competing reaction between and peroxide can be detected up to a 10-fold excess of peroxide over 9,10-dihydroanthracene. 相似文献
10.
Under anaerobic conditions, ethyl hydroperoxide functions as a two-electron acceptor in the tyrosinase-catalyzed oxidation of 4-tert-butylcatechol to 4-tert-butyl-o-benzoquinone, apparently by the following mechanism: This is a direct demonstration of the pseudoperoxidase activity of tyrosinase. Ethyl hydroperoxide failed to oxidize either oxy- or deoxyhemocyanin. 相似文献
11.
N-Phenylhydroxylamine is oxidized in aqueous phosphate buffer to nitrosobenzene, nitrobenzene, and azoxybenzene. Degradation is O2 dependent and shows general catalysis by (k1 = 2.3 M?2 sec?1) and (k2 = 2.3 × 105M?2 sec?1) or kinetically equivalent terms. Evidence is presented suggesting the intermediacy of a highly reactive species leading to these products. 相似文献
12.
Peter Nicholls 《BBA》1976,430(1):13-29
1. Formate inhibits cytochrome oxidase activity both in intact mitochondria and submitochondrial particles, and in isolated cytochrome . 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 ) and in the half-reduced species (). Comparison with cyanide-induced spectral shifts, towards the red, indicates that formate and cyanide have opposite effects on the spectrum, both in the fully oxidized and the half-reduced states. The formate spectra provide a new method of obtaining the difference spectrum of minus , free of the difficulties with cyanide (which induces marked high → low spin spectral shifts in cytochrome ) and azide (which induces peak shifts of cytochrome towards the blue in both α- and Soret regions).3. The rate of formate dissociation from cytochrome is faster than its rate of dissociation from , especially in the presence of cytochrome . The 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 °C.4. Succinate-cytochrome reductase activity is also inhibited by formate, in a reaction competitive with succinate and dependent on [formate]2.5. Formate inhibition of ascorbate plus 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 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 level and to a slow extra inhibition by formate following uncoupler addition, indicating a third site of formate action in the intact mitochondrion. 相似文献
13.
E.M. Kosower 《Biochemical and biophysical research communications》1980,92(2):356-364
A new mechanism that involves dissociative electron transfer in the energy transducing step is set forward for bacterial luciferase catalyzed light emission. The proposal involves (1) dissociation of the 4a-hydroperoxyflavin to a flavin radical and , accounting for 570 and 620nm absorption, (2) addition to the aldehyde carbonyl to form a peroxyl radical, (3) abstraction of H from an enzyme thiol group to form RCH(OOH)OH, (4) thiyl radical abstraction of the H on C in RCH(OOH)OH, a step which can show a of ca. 4, and (5) dissociative electron- transfer, a highly exothermic step that leads to a protonated flavin excited state, a carboxylic acid and water. 相似文献
14.
Hiroshi Maeda Takaaki Kishi Shoichi Ikeda Susumu Sasaki Kyoji Kito 《International journal of biological macromolecules》1983,5(3):159-162
Precipitation of human fibrinogen in 0.15 m NaCl occurred at pH 7.4 (Tris-HCl buffer) when ZnCl2, CuCl2, NiCl2, or CoCl2 were added beyond their respective critical concentrations. The critical concentrations were about . At pH 5.8 2-(N-morpholino)-ethane sulphonic acid buffer, the critical concentrations were found only for CuCl2 and ZnCl2, and were about , respectively. CaCl2 and MgCl2 were not effective up to at pH 7.4 and 5.8, respectively. At pH 7.4, precipitation was better in 0.015 m NaCl than in 0.15 m NaCl for both CuCl2 and ZnCl2. Little or no conformational change was indicated on binding Cu2+ ions. The fluorescence of tryptophan was quenched only by CuCl2, while other metal ions (ZnCl2, NiCl2, CoCl2 and CaCl2) were ineffective as quenchers. 相似文献
15.
The cell-free preparations from autotrophieally grown Pseudomonas saccharophila catalyzed the process of electron transport from H2 or various other organic electron donors to either O2 or NO3? with concomitant ATP generation. The respective ratios with H2 and NADH were 0.63 and 0.73, the respective ratios were 0.57 and 0.54. In contrast, the and ratios with succinate were 0.18 and 0.11, respectively. ATP formation coupled to the oxidation of ascorbate, in the absence or presence of added N,N,N′,N′-tetramethyl-p-phenylenediamine or cytochrome c, could not be detected. Various uncouplers inhibited phosphorylation with either O2 or NO3? as terminal electron acceptors without affecting the oxidation of H2 or other substrates. The NADH oxidation at the expense of O2 or NO3? reduction as well as the associated phosphorylation were inhibited by rotenone and amytal. The aerobic and anaerobic H2 oxidation and coupled ATP synthesis, on the other hand, was unaffected by the flavoprotein inhibitors as well as by the NADH trapping system. The NADH, H2, and succinate-linked electron transport to O2 or NO3? and the associated phosphorylations were sensitive, however, to antimycin A or 2-n-nonyl-4-hydroxyquino-line-N-oxide, and cyanide or azide. The data indicated that although the phosphorylation sites 1 and II were associated with NADH oxidation by O2 or NO3?, the energy conservation coupled to H2 oxidation under aerobic or anaerobic conditions appeared to involve site II only. 相似文献
16.
Lutz Thilo 《生物化学与生物物理学报:生物膜》1977,469(3):326-334
In an accompanying publication by Duckwitz-Peterlein, Eilenberger and Overath ((1977) Biochim. Biophys. Acta 469, 311–325) it is shown that the exchange of lipid molecules between negatively charged vesicles consisting of total phospholipid extracts from Escherichia coli occurs by the transfer of single lipid monomers or small micelles through the water. Here a kinetic interpretation is presented in terms of a rate constant, , for the escape of lipid molecules from the vesicle bilayer into the water. The evaluated rate constants are and for phospholipid molecules with and , respectively, as the predominant acyl chain component. The rate constants are discussed in terms of the acyl chain and polar head group composition of the lipids. 相似文献
17.
F.M.A.H. Schuurmans Stekhoven H.G.P. Swarts Y.-F. Fu G.A.J. Kuijpers J.J.H.H.M. de Pont S.L. Bonting 《生物化学与生物物理学报:生物膜》1984,774(2):277-287
(1) Treatment of from rabbit kidney outer medulla with the labeled thio-analogue of ATP in the presence of and the absence of K+ leads to thiophosphorylation of the enzyme. The value for [γ-S]ATP is 2.2 μM and for Na+ 4.2 mM at 22°C. Thiophosphorylation is a sigmoidal function of the Na+ concentration, yielding a Hill coefficient . (2) The thio-analogue () can also support overall activity, but at 37°C is only h?1 or 0.09% of the specific activity for ATP (). (3) The thiophosphoenzyme intermediate, like the natural phosphoenzyme, is sensitive to hydroxylamine, indicating that it also is an acylphosphate. However, the thiophosphoenzyme, unlike the phosphoenzyme, is acid labile at temperatures as low as 0°C. The acid-denatured thiophosphoenzyme has optimal stability at pH 5–6. (4) The thiophosphorylation capacity of the enzyme is equal to its phosphorylation capacity, indicating the same number of sites. Phosphorylation by ATP excludes thiophosphorylation, suggesting that the two substrates compete for the same phosphorylation site. (5) The (apparent) rate constants of thiophosphorylation (0.4 s?1 vs. 180 s?1), spontaneous dethiophosphorylation (0.04 s?1 vs. 0.5 s?1) and K+-stimulated dethiophosphorylation (0.54 s?1 vs. 230 s?1) are much lower than those for the corresponding reactions based on ATP. (6) In contrast to the phosphoenzyme, the thiophosphoenzyme is ADP-sensitive (with an apparent rate constant in ADP-induced dethiophosphorylation of 0.35 s?1, ) and is relatively K+-insensitve. The for K+ in dethiophosphorylation is 0.9 mM and in dephosphorylation 0.09 mM. The thiophosphoenzyme appears to be for 75–90% in the ADP-sensitive E1-conformation. 相似文献
18.
The concept of high- and low-affinity reactions in bovine cytochrome c oxidase steady-state kinetics
(1) Analysis of the data from steady-state kinetic studies shows that two reactions between cytochrome c and cytochrome c oxidase sufficed to describe the concave Eadie-Hofstee plots ( and ). It is not necessary to postulate a third reaction of . (2) Change of temperature, type of detergent and type of cytochrome c affected both reactions to the same extent. The presence of only a single catalytic cytochrome c interaction site on the oxidase could explain the kinetic data. (3) Our experiments support the notion that, at least under our conditions (pH 7.8, low-ionic strength), the dissociation of ferricytochrome c from cytochrome c oxidase is the rate-limiting step in the steady-state kinetics. (4) A series of models, proposed to describe the observed steady-state kinetics, is discussed. 相似文献
19.
The uptake of radiolabeled carnitine and butyrobetaine has been studied in human heart cells (CCL 27). The uptake of carnitine is 3–10-fold higher in heart cells than in fibroblasts (). The uptake of carnitine increases with temperature coefficient of 1.6 in the interval 10–20° C and with a negligible uptake at 4 and 10° C. The uptake of carnitine follows Michaelis-Menten kinetics with a of and . Carnitine uptake is suppressed 90% by NaF (24 mM). Butyrobetaine is taken up into heart cells to the same extent as carnitine with a of 5.7–17.3 μM and . Butyrobetaine inhibits competitively the uptake of carnitine and carnitine inhibits the uptake of butyrobetaine to the same extent. No conversion of radiolabeled butyrobetaine to carnitine, or carnitine to methyl choline was observed intra- or extracellulary during incubation. These data are compatible with a selective transport mechanism for carnitine which is also responsible for the uptake of butyrobetaine. 相似文献
20.
W.McD. Armstrong W.R. Bixenman K.F. Frey J.F. Garcia-Diaz M.G. ORegan Jeanie L. Owens 《生物化学与生物物理学报:生物膜》1979,551(1):207-219
Na+, K+ and Cl? concentrations () and activities (), and mucosal membrane potentials () were measured in epithelial cells of isolated bullfrog (Rana catesbeiana) small intestine. Segments of intestine were stripped of their external muscle layers, and bathed (at 25°C and pH 7.2) in oxygenated Ringer solutions containing 105 mM Na+ and Cl? and 5.4 mM K+. Na+ and K+ concentrations were determined by atomic absorption spectrometry and Cl? concentrations by conductometric titration following extraction of the dried tissue with 0.1 M HNO3. 14C-labelled inulin was used to determine extracellular volume. was measured with conventional open tip microelectrodes, with solid-state Cl?-selective silver microelectrodes and and with Na+- and K+-selective liquid ion-exchanger microelectrodes. The average recorded was ?34 mV. , and were 51, 105 and 52 mM. The corresponding values for , and were 18, 80 and 33 mM. These results suggest that a large fraction of the cytoplasmic Na+ is ‘bound’ or sequestered in an osmotically inactive form, that all, or virtually all the cytoplasmic K+ behaves as if in free solution, and that there is probably some binding of cytoplasmic Cl?. significantly exceeds the level corresponding to electrochemical equilibrium across the mucosal and baso-lateral cell membranes. Earlier studies showed that coupled mucosal entry of Na+ and Cl? is implicated in intracellular Cl? accumulation in this tissue. This study permitted estimation of the steady-state transapical Na+ and Cl? electrochemical potential differences (Δμ̄Na and Δμ̄Cl). Δμ̄Na (?7000 J · mol?1; cell minus mucosal medium) was energetically more than sufficient to account for Δμ̄Cl (1000–2000 J · mol?1). 相似文献