共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
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
3.
The immobilization of Rhodopseudomonas capsulata chromatophores by entrapment in an alginate gel is described. Alginate beads were prepared with Ba2+, Sr2+ and Ca2+ as gel-forming agents and compared for their mechanical strength, chemical resistance against disruption by phosphate-induced swelling, and yield of photophosphorylation activity. Barium alginate beads proved to have better physico-chemical properties than the more commonly used calcium alginate beads. After embedding in barium alginate gel, R. capsulata chromatophores retained a high yield (up to 70%) of their photophosphorylation capacity. Alginate entrapment did not cause a large increase in the Michaelis constant for ADP and phosphate, the substrates of adenosinetriphosphatase (ATPase). These constants were and for free chromatophores and and for chromatophores entrapped in barium alginate gel. However, embedding gave no additional protection against rapid inactivation of chromatophores upon storage at 3°C. Preliminary results with a batch reactor for continuous ATP regeneration are presented. The barium alginate method has two features which are not generally encountered at the same time, extremely mild conditions for entrapment and excellent physical properties of the gels beads, which make this method a suitable tool for the construction of bioreactors with immobilized cells or organelles. 相似文献
4.
Interaction of lymphocytes and macrophage cell line cells (M1 cells). I. Functional maturation and appearance of Fc receptors im M1 cells 总被引:2,自引:0,他引:2
M1 cells, which are cell line cells established from myeloid leukemia cells of the SL strain mouse, can differentiate from blast cells () to mature macrophages () within 48 hr, when they are cultured with conditioned medium (CM) obtained from murine embryonic fibroblasts. While cells have no phagocytic activity nor Fc receptor (FcR), cells possess both characteristics. The appearance of FcR is temperature-dependent and inhibited by a metabolic inhibitor, cycloheximide. FcR on cells is resistant to trypsin and pronase. cells improve the viability of macrophage-depleted SL splenic lymphocytes and restore the in vitro secondary plaque forming cell response of macrophage-depleted spleen cells to particulate and soluble antigens. cells lack this macrophage-substituting capacity. Mm1 cells, mutant cells from M1 cells, having FcR and higher phagocytic activity than cells, are also devoid of this capacity. 相似文献
5.
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
6.
R S Himmelwright N C Eickman E I Solomon 《Biochemical and biophysical research communications》1978,84(2):300-305
Half hemocyanin is shown to undergo a unique change at the Cu(II)?Cu(I) active site with temperature, exhibiting class II mixed valent properties at low temperature (The appearance of an intense near IR intervalence-transfer transition and a delocalized EPR spectrum). This requires a Cu(II)NNNCu(I) bridging geometry. The effects of CO coordination to half , combined with the presence of a low energy charge transfer transition, demonstrate that azide is also bridging at room temperature. Finally, half is found to be capable of coordination of a second at the copper(II) site. 相似文献
7.
The apparent Arrhenius energy of activation () of the water osmotic permeability () of the basolateral plasma cell membrane of isolated rabbit proximal straight tubules has been measured under control conditions and after addition of 2.5 mM of the sulfhydryl reagent, para-chloromercuribenzenesulfonic acid (pCMBS), of mersalyl and of dithiothreitol. (kcal/mol) was (controls) and (pCMBS), while decreased with pCMBS to of its control value. Mersalyl also decreased both in vitro and in vivo (using therapeutical doses). These actions of pCMBS and mersalyl were quickly reverted with 5 mM dithiothreitol and prevented by 0.1 M thiourea. for free viscous flow is 4.2 and greater than 10 for non-pore-containing lipid membranes. By analogy with these membranes and with red blood cells, where similar effects of pCMBS on are observed, it is concluded that cell membranes of the proximal tubule are pierced by aqueous pores which are reversibly shut by pCMBS. Part of the action of mercurial diuretics can be explained by their action on . 相似文献
8.
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
9.
The oxidation of unsaturated fatty acid micelles by the superoxide free radical (), during γ irradiation in the presence of formate, is kinetically distinct from oxidation by hydroxyl free radicals (HO.). The evidence suggests that a direct reaction between () and lipid hydroperoxide initiates a chain oxidation process in the micelles. While tetranitromethane, which reacts rapidly with (), protects the micelles from oxidation, active superoxide dismutase is no more effective than its apoprotein, due to lack of penetration of the micellar environment. We discuss these findings in the light of recent literature, and with reference to their possible significance for biological systems. 相似文献
10.
(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
11.
T R Green R E Schaefer M T Makler 《Biochemical and biophysical research communications》1980,94(4):1213-1220
In many instances the effect of superoxide () trapping agents in suppressing the net rate of O2 consumption of activated PMN's is not in accordance with theoretical expectations. We offer here an alternate explanation to those previously presented by Segal and Meshulam (FEBS Letters 100, 27–32) and Babior (Biochem. Biophys. Res. Comm. 91, 222–226). The paradoxical results previously presented can be explained by recognizing that shortly after activation of resting cells an O2 diffusion layer is established at or near the outer surface of these cells. The presence of this diffusion layer can markedly alter the anticipated stochiometric relationship between trapped and apparent O2 consumed by these cells when they are exposed to trapping agents. 相似文献
12.
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
13.
14.
R C Warrington 《Analytical biochemistry》1974,62(1):204-216
A general procedure for the isolation of 3′-linked fragments derived from tRNA molecules is described. Purified N-2-naphthoxyacetylglycyl derivatives of the and of yeast were exhaustively digested with RNase T1 and the 3′-linked fragments (bearing the derivative) were separated from other degradation products (lacking the derivative) by stepwise chromatography on BD-cellulose. Subsequent chromatographic resolution and base-composition analysis allowed tentative identification of the 3′-terminals of and as Gp(Cp,Ap)CpCpA and Gp(Cp,Cp,Up,Ap)CpCpA, respectively. The potential utility of this procedure for development of a novel approach to nucleic acid sequence analysis is discussed. 相似文献
15.
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
16.
The reactivities of anionic nitroalkanes with 2-nitropropane dioxygenase of Hansenula mrakii, glucose oxidase of Aspergillus niger, and mammalian d-amino acid oxidase have been compared kinetically. 2-Nitropropane dioxygenase is 1200 and 4800 times more active with anionic 2-nitropropane than d-amino acid oxidase and glucose oxidase, respectively. The apparent Km values for anionic 2-nitropropane are as follows: 2-nitropropane dioxygenase, 1.61 mm; glucose oxidase, 16.7 mm; and d-amino acid oxidase, 11.1 mm. Anionic 2-nitropropane undergoes an oxygenase reaction with 2-nitropropane dioxygenase and glucose oxidase, and an oxidase reaction with d-amino acid oxidase. In contrast, anionic nitroethane is oxidized through an oxygenase reaction by 2-nitropropane dioxygenase, and through an oxidase reaction by glucose oxidase. All nitroalkane oxidations by these three flavoenzymes are inhibited by Cu and Zn-superoxide dismutase of bovine blood, Mn-superoxide dismutases of bacilli, Fe-superoxide dismutase of Serratia marcescens, and other scavengers such as cytochrome c and NADH, but are not affected by hydroxyl radical scavengers such as mannitol. None of the scavengers tested affected the inherent substrate oxidation by glucose oxidase and d-amino acid oxidase. Furthermore, the generation of in the oxidation of anionic 2-nitropropane by 2-nitropropane dioxygenase was revealed by ESR spectroscoy. The ESR spectrum of anionic 2-nitropropane plus 2-nitropropane dioxygenase shows signals at g1 = 2.007 and g11 = 2.051, which are characteristic of . The generated is a catalytically essential intermediate in the oxidation of anionic nitroalkanes by the enzymes. 相似文献
17.
Commercial [5-14C]mevalonate is shown to contain several radioactive impurities, which give artifactually high amounts of Hyamine bound, volatile acidic radioactivity when incubated with killed or living rat renal cortex slices, as compared with [5-14C]mevalonate purified either by liquid-liquid partition chromatography or through the enzymically generated by ion-exchange chromatography. The artifactual results were not diluted by incubation with increasing amounts of unlabelled mevalonate, whereas the and []cholesterol produced by rat renal cortex slices incubated with purified [5-14C]mevalonate were both diluted to the same extent by unlabelled mevalonate. It is concluded that is genuinely oxidized to , and that purification of substrate before its use is necessary. Production of and various []lipids from purified [5-14C]mevalonate, as a function of time and substrate concentration, by renal cortex and liver slices, is described. 相似文献
18.
The changes in polymer-solvent interactions that occur when native calf thymus DNA is dialyzed against Na2SO4 solutions of a given ionic strength and buffer concentration but of varying concentrations in methylmercuric hydroxide have been investigated with the help of solution density measurements at 25 °C and pH 6.8–7.0. From measurements executed under equilibrium dialysis conditions at the three salt levels 5 mm, 0.05 m, and 0.5 m Na2SO4 (m refers to molality) and in the presence of 5 mm cacodylic acid buffer, the density increments for native calf thymus DNA were determined as a function of CH3HgOH concentration. was found not to vary with organomercurial concentration, irrespective of the concentration of supporting electrolyte, until a certain CH3HgOH concentration level has been reached, viz., , beyond which increases strongly with increasing concentration of CH3HgOH. As is shown by optical melting, becomes a function of organomercurial concentration the moment DNA undergoes denaturation brought about by the complexing of CH3HgOH with the various N-binding sites of the base residues in the DNA double helix.Polymer-solvent interactions, expressed in terms of preferential water interactions (“net hydration”) and preferential salt interactions (“salt solvation”), were derived from the data in combination with data obtained on the preferential interaction of CH3HgOH with denatured DNA and data on the partial specific volumes of all major solution components, gathered from density measurements on solutions with fixed concentrations of diffusible components. Evidence is presented which shows that denaturation in general decreases the net hydration while salt becomes preferentially associated with the polyelectrolyte. This process is further amplified by the interaction of CH3HgOH with denatured DNA: Methylmercurated DNA alters the redistribution of diffusible components at dialysis equilibrium to such an extent that in a formal sense large amounts of water are rejected from the immediate vicinity of the polymer. The molecular implications of these findings are explored. The results are further discussed in the light of previous findings where the methylmercury-induced denaturation of DNA had been studied with the help of buoyant density measurements in a Cs2SO4 density gradient and by velocity-sedimentation in a variety of sulfate media. 相似文献
19.
Bernard Lacour Tilman Drüeke Evelyne Pierandreï Bernadette Nabarra Jean-Louis Funck-Brentano 《生物化学与生物物理学报:生物膜》1981,648(2):151-161
Parathyroid hormone (PTH) and calcitonin exert well known effects on the renal tubule which are thought to involve specific hormone receptors and adenyl cyclase. In the intestine, it is not clear whether the action of PTH and calcitonin is only indirect or also direct, and their mechanisms of action are much less well established. In the present study, possibly direct effects of PTH and calcitonin on Na+ transport in isolated intestinal epithelial cells of rats were investigated. In the presence of bovine PTH (1.2 I.U./ml) in the incubation medium, the Na+ efflux rate constant () of isolated enterocytes was significantly reduced when compared to that in control experiments with the hormone vehicle only. The mean depression of induced by bovine PTH was 26% as compared to the control (100%) and to that induced by ouabain (4.0mM) which was 44%. No depressant effect of bovine PTH on was observed when the isolated enterocytes were incubated with ouabain (4.0 mM). Thus, bovine PTH appeared to inhibit the ouabain-sensitive Na+ pump. When incubating the isolated epithelial cells in an EGTA-containing Ca2+-free medium, bovine PTH lost its capacity to inhibit (). Thus, the presence of extracellular Ca2+ appeared necessary for the inhibitory effect of bovine PTH. In contrast to its effect on , bovine PTH induced no change in net Na+ uptake by isolated enterocytes. Moreover, no significant effect on enterocyte Na+ transport could be demostrated for salmon or porcine calcitonin at two different concentrations in the incubation medium. Neither bovine PTH nor salmon calcitonin induced significant changes in enterocyte cyclic AMP or cyclic GMP concentrations. It was concluded that bovine PTH, but not calcitonin, exerted a direct inhibitory effect on the ouabain-sensitive of isolated rat enterocytes. The effect of bovine PTH occured without measurable activation of the cyclic nucleotide system but needed the presence of Ca2+ in the incubation medium to be operative. 相似文献
20.
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