共查询到20条相似文献,搜索用时 15 毫秒
1.
《BBA》1986,849(3):355-365
Rapid CO2 gas exchange by Helianthus leaves was analysed kinetically using a computer model which distinguished different components of the gas exchange by different time constants. A rapid phase of CO2 uptake was ascribed to the solubilization of CO2 in all leaf compartments and to the conversion of the dissolved CO2 to HCO3− in the chloroplast stroma which contains carbonic anhydrase. From stromal ratios the stroma pH of darkened leaves was estimated to be close to 7.5. Occasionally, values as high as 8 or as low as 7 were also obtained. If fast HCO3− formation also occurs in the cytosol, pH values may be lower by about 0.3 pH units than those calculated under the assumption that carbonic anhydrase is localized in chloroplasts only. Illumination with a light intensity close to saturation of photosynthesis caused an increase in CO2 solubilization which indicated the alkalization of the chloroplast stroma by about 0.6 pH units. This is an underestimation, if the pH of cytosol decreases in the light liberating CO2 by the action of carbon anhydrase. An alkalization of the stroma by 0.6 pH units indicates the export of about 450 nmol H+/mg chlorophyll from the stroma. This forms the basis of a large transthylakoid pH gradient which drives light-dependent ATP synthesis. A pH gradient between stroma and cytosol is capable of supporting secondary gradients between these compartments in the light, such as a gradient in the ratio. On darkening, the stroma alkalization was reversed. The rate of stroma acidification was much higher in the presence of CO2 than in its absence. 相似文献
2.
Chloroplasts which were rapidly isolated from illuminated leaves showed activity of ATP hydrolysis at a level much higher than that of the dark control. Under the high-intensity illumination or under repetitive flash excitation, the activated chloroplasts synthesized more ATP than those with a low ATP hydrolysis activity. formed under repetitive flashes was smaller in the activated chloroplasts than in the inactive chloroplasts. The inhibition of ATP yield per flash by valinomycin or nigericin in the presence of K+ was stronger in the inactive chloroplasts than in the activated chloroplast. ATP synthesis in the activated chloroplasts seems to have a lower threshold. 相似文献
3.
Chana Vinkler 《Biochemical and biophysical research communications》1981,99(4):1095-1100
The of ADP for photophosphorylation in lettuce chloroplasts was measured both at various light intensities and in the presence of various uncoupler (nigericin + K+) concentrations. Lowering the light intensity results in both, a decrease in the rate of phosphorylation and a several fold in the of ADP for the reaction. However, when increasing concentrations of the uncoupler nigericin + K+ are employed, the rate of photophosphorylation is decreased but a several-fold in the of ADP for the reaction is observed. The results are discussed in terms of the chemiosmotic hypothesis. It is suggested that these effects might indicate the existence of a mechanism controlling the rate of ATP formation which is different than the formation of the electrochemical gradient. 相似文献
4.
5.
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
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7.
[] Phosphatidylcholines are introduced into the outer monolayer of phosphatidylcholine vesicles with the phosphatidylcholine exchange protein from bovine liver. The transbilayer distribution of the [] phosphatidylcholine is measured with 13C NMR. The transbilayer movements of phosphatidylcholine and [] dimyristoyl phosphatidylcholine at 30°C in vesicles composed of these phosphatidylcholines are extremely slow processes with estimated half-times of days. [] Dioleoyl phosphatidylcholine introduced into dimyristoyl phosphatidylcholine vesicles migrates from the outer to the inner monolayer with a half-time of less than 12 h. The data suggest that differential changes in the lateral packing of the two monolayers might be a driving force for transbilayer transport of phospholipids. 相似文献
8.
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
9.
G.D. Holman 《生物化学与生物物理学报:生物膜》1978,508(1):174-183
10?5 M cyclic AMP has high permeability in human erythrocyte ghosts (). Saturation of influx and efflux occurs. . . . at 30°C. Equilibrium exchange entry of cyclic AMP has similar kinetics to zero trans influx, though the system does show counterflow. Cythochalasin B is an apparent competitive inhibitor of cyclic AMP exit. ().Control experiments indicated that cyclic AMP remains intact during incubation with red blood cell ghosts and is contained within the intravesicular space during the transport experiments. 相似文献
10.
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
11.
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
12.
Delocalized chemiosmotic coupling of oxidative phosphorylation requires that a single-value correlation exists between the extent of and the kinetic parameters of respiration and ATP synthesis. This expectation was tested experimentally in nigericin-treated plant mitochondria in single combined experiments, in which simultaneously respiration (in State 3 and in State 4) was measured polarographically, FΔψ (which under these conditions was equivalent to ) was evaluated potentiometrically from the uptake of tetraphenylphosphonium+ and the rate of phosphorylation was estimated from the transient depolarization of mitochondria during State 4-State 3-State 4 transitions. The steady-state rates of the different biochemical reactions were progressively inhibited by specific inhibitors active with different modalities on various steps of the energy-transducing process: succinate respiration was inhibited competitively with malonate or noncompetitively with antimycin A, or by limiting the rate of transport into the mitochondria of the respiratory substrate with phenylsuccinate; was dissipated by uncoupling with increasing concentrations of valinomycin; ADP phosphorylation was limited with oligomycin. The results indicate generally that when the rate of respiratory electron flow is decreased, a parallel inhibition of the rate of phosphorylation is also observed, while very limited effects can be detected on the extent of . This behavior is in marked contrast to the effect of uncoupling where the decreased rate of ATP synthesis is clearly due to energy limitation. Extending previous observations in bacterial photosynthesis and in respiration by animal mitochondria and submitochondrial particles the results indicate, therefore, that respiration tightly controls the rate of ATP synthesis, with a mechanism largely independent of . These data cannot be reconciled with a delocalized chemiosmotic coupling model. 相似文献
13.
The kinetics of isotopic Na+ flows was studied in urinary bladders of toads from the Dominican Republic. Initial studies of the potential dependence of passive serosal to mucosal 22Na+ efflux demonstrated the absence of isotope interaction and/or other coupling with passive Na+ flow. The electrical current and mucosal to serosal 22Na+ influx were then measured with transmembrane potential clamped at . Subsequent elimination of active Na+ transport mucosal amiloride permitted calculation of the rates of active Na+ transport and active and passive influx and and . The results indicate that for Dominican toad bladders mounted in chambers only Na+ contributes significantly to transepithelial active ion transport; hence . was abolished at . As Δψ approached , active efflux became demonstrable. At exceeded , so that was negative. Experimental values of agreed well with theoretical values predicted by a thermodynamic formulation: . The dependence of on Δψ is curvilinear. 相似文献
14.
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
15.
B M Babior 《Biochemical and biophysical research communications》1979,91(1):222-226
The widely held view that stimulated phagocytes liberate into the extracellular medium is supported by the alterations in oxygen uptake which occur when ferricytochrome is added to a suspension of zymosan-treated neutrophils. An explanation consistent with this view is provided for some previously reported results , 27) which initially appeared to conflict with the notion that is released by phagocytes. 相似文献
16.
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
17.
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
18.
W R Scowcroft A H Gibson J D Pagan 《Biochemical and biophysical research communications》1976,73(2):516-523
Nitrogenase activity in agar cultures of cowpea rhizobia, strain 32H1, was rapidly inhibited by but this was relieved by increased O2 tension. Inhibition was more rapid than that caused by inhibitors of protein synthesis and was not relieved by methionine sulfoximine or methionine sulfone. Under conditions were nitrogenase activity was inhibited by , glutamine synthetase and glutamate synthase were substantially unaffected. Glutamate dehydrogenase was undetected in either nitrogenase active or inhibited cultures. These results indicate that inhibition of nitrogenase activity in strain 32H1 is not effected through glutamine synthetase regulation of nitrogenase synthesis. 相似文献
19.
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
20.
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