Página 5 dos resultados de 686 itens digitais encontrados em 0.011 segundos

Sites of Inhibition by Disulfiram in Thylakoid Membranes 1

Blubaugh, Danny J.; Govindjee
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1988 EN
Relevância na Pesquisa
57.31831%
Disulfiram (tetraethylthiuram disulfide), a metal chelator, inhibits photosynthetic electron transport in broken chloroplasts. A major site of inhibition is detected on the electron-acceptor side of photosystem II between QA, the first plastoquinone electron-acceptor, and the second plastoquinone electron-acceptor, QB. This site of inhibition is shown by a severalfold increase in the half-time of Q−A oxidation, as monitored by the decay of the variable chlorophyll a flourescence after an actinic flash. Another site of inhibition is detected in the functioning of the reaction center of photosystem II; disulfiram is observed to quench the room temperature variable chlorophyll a fluorescence, as well as the intensity of the 695 nm peak, relative to the 685 nm peak, in the chlorophyll a fluorescence spectrum at 77 K. Electron transport from H2O to the photosystem II electron-acceptor silicomolybdate is also inhibited. Disulfiram does not inhibit electron flow before the site(s) of donation by exogenous electron donors to photosystem II, and no inhibition is detected in the partial reactions associated with photosystem I.

Anion-Sensitive Mg2+ ATP-Dependent Proton Pumping in Microsomal Membranes from Phycomyces blakesleeanus Bgff

Rausch, Thomas; Soffel, Sigrid; Hilgenberg, Willy
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1988 EN
Relevância na Pesquisa
57.33362%
A light microsomal membrane fraction (collected on 28% weight/volume sucrose) from young mycelia of Phycomyces blakesleeanus Bgff. stationary cultures exhibited Mg2+ ATP-dependent proton pumping as monitored with the dye neutral red or by accumulation of [14C]methylamine. The substrate kinetics for ATP (Km(ATP) 1.1 millimolar in the presence of 2 millimolar Mg2+), the competitive inhibition by ADP (Ki(ADP) 0.8 millimolar), the anion sensitivity (stimulation by Cl−, inhibition by NO3− and SO42−), the reversal of acidification by Ca2+, the inhibition by diethylstilbestrol and dicyclohexylcarbodiimide, as well as the absence of any inhibition by azide, molybdate, and vanadate strongly suggest a tonoplast-type ATPase driven proton pumping. The same membrane fraction showed no pyrophosphate driven H+-translocation. Electron microscopic examination of the fungal mycelium demonstrated the presence of vacuoles of different sizes and other nonidentified vesicles but no typical Golgi stacks.

Inactive Photosystem II Complexes in Leaves 1: Turnover Rate and Quantitation

Chylla, Roger A.; Whitmarsh, John
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1989 EN
Relevância na Pesquisa
57.33362%
The flash-induced electrochromic shift, measured by the amplitude of the rapid absorbance increase at 518 nanometers (ΔA518), was used to determine the amount of charge separation within photosystems II and I in spinach (Spinacia oleracea L.) leaves. The recovery time of the reaction centers was determined by comparing the amplitudes of ΔA518 induced by two flashes separated by a variable time interval. The recovery of the ΔA518 on the second flash revealed that 20% of the reaction centers exhibited a recovery half-time of 1.7 ± 0.3 seconds, which is 1000 times slower than normally active reaction centers. Measurements using isolated thylakoid membranes showed that photosystem I constituted 38% of the total number of reaction centers, and that the photosystem I reaction centers were nearly fully active, indicating that the slowly turning over reaction centers were due solely to photosystem II. The results demonstrate that in spinach leaves approximately 32% of the photosystem II complexes are effectively inactive, in that their contribution to energy conversion is negligible. Additional evidence for inactive photosystem II complexes in spinach leaves was provided by fluorescence induction measurements, used to monitor the oxidation kinetics of the primary quinone acceptor of photosystem II...

Selective Delipidation of the Plasma Membrane by Surfactants 1: Enrichment of Sterols and Activation of ATPase

Sandstrom, Richard P.; Cleland, Robert E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1989 EN
Relevância na Pesquisa
57.327437%
The influence of plasma membrane lipid components on the activity of the H+-ATPase has been studied by determining the effect of surfactants on membrane lipids and ATPase activity of oat (Avena sativa L.) root plasma membrane vesicles purified by a two-phase partitioning procedure. Triton X-100, at 25 to 1 (weight/weight) Triton to plasma membrane protein, an amount that causes maximal activation of the ATPase in the ATPase assay, extracted 59% of the membrane protein but did not solubilize the bulk of the ATPase. The Triton-insoluble proteins had associated with them, on a micromole per milligram protein basis, only 14% as much phospholipid, but 38% of the glycolipids and sterols, as compared with the native membranes. The Triton insoluble ATPase could still be activated by Triton X-100. When solubilized by lysolecithin, there were still sterols associated with the ATPase fraction. Free sterols were found associated with the ATPase in the same relative proportions, whether treated with surfactants or not. We suggest that surfactants activate the ATPase by altering the hydrophobic environment around the enzyme. We propose that sterols, through their interaction with the ATPase, may be essential for ATPase activity.

Stoichiometry of Photosystem I, Photosystem II, and Phycobilisomes in the Red Alga Porphyridium cruentum as a Function of Growth Irradiance 1

Cunningham, Francis X.; Dennenberg, Ronald J.; Mustardy, Laszlo; Jursinic, Paul A.; Gantt, Elisabeth
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1989 EN
Relevância na Pesquisa
57.069224%
Cells of the red alga Porphyridium cruentum (ATCC 50161) exposed to increasing growth irradiance exhibited up to a three-fold reduction in photosystems I and II (PSI and PSII) and phycobilisomes but little change in the relative numbers of these components. Batch cultures of P. cruentum were grown under four photon flux densities of continuous white light; 6 (low light, LL), 35 (medium light, ML), 180 (high light, HL), and 280 (very high light, VHL) microeinsteins per square meter per second and sampled in the exponential phase of growth. Ratios of PSII to PSI ranged between 0.43 and 0.54. About three PSII centers per phycobilisome were found, regardless of growth irradiance. The phycoerythrin content of phycobilisomes decreased by about 25% for HL and VHL compared to LL and ML cultures. The unit sizes of PSI (chlorophyll/P700) and PSII (chlorophyll/QA) decreased by about 20% with increase in photon flux density from 6 to 280 microeinsteins per square meter per second. A threefold reduction in cell content of chlorophyll at the higher photon flux densities was accompanied by a twofold reduction in β-carotene, and a drastic reduction in thylakoid membrane area. Cell content of zeaxanthin, the major carotenoid in P. cruentum, did not vary with growth irradiance...

Measurement of Net Fluxes of Ammonium and Nitrate at the Surface of Barley Roots Using Ion-Selective Microelectrodes 1

Henriksen, Gordon H.; Bloom, Arnold J.; Spanswick, Roger M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1990 EN
Relevância na Pesquisa
57.069224%
Neutral carrier-based liquid membrane ion-selective microelectrodes for NH4+ and NO3− were developed and used to investigate inorganic nitrogen acquisition in two varieties of barley, Hordeum vulgare L. cv Olli and H. vulgare L. cv Prato, originating in cold and warm climates, respectively. In the present paper, the methods used in the fabrication of ammonium- and nitrate-selective microelectrodes are described, and their application in the study of inorganic nitrogen uptake is demonstrated. Net ionic fluxes of NH4+ and NO3− were measured in the unstirred layer of solution immediately external to the root surface. The preference for the uptake of a particular ionic form was examined by measuring the net flux of the predominant form of inorganic nitrogen, with and without the alternative ion in solution. Net flux of NH4+ into the cold-adapted variety remained unchanged when equimolar concentrations (200 micromolar) of NH4+ and NO3− were present. Similarly, net flux of NO3− into the warm-adapted variety was not affected when NH4+ was also present in solution. The high temporal and spatial resolution afforded by ammonium- and nitrate-selective microelectrodes permits a detailed examination of inorganic nitrogen acquisition and its component ionic interactions.

Sulfhydryl Reagents and Energy-Linked Reactions in Monocot Thylakoids 1

Cohen, William S.; Baxter, Donald R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1990 EN
Relevância na Pesquisa
57.33362%
Monofunctional maleimides have been used to covalently modify the coupling factor protein of monocot thylakoid membranes. As with dicot thylakoids, incubation of the monocot thylakoids with maleimides in the light but not in the dark results in inhibition of both ATP synthesis and hydrolysis. In the dark, sites on the γ and ε subunits of maize Zea mays coupling factor 1 are modified after incubation of maize mesophyll thylakoids with the fluorescent maleimide N-(anilinonaphthyl-4) maleimide. A light accessible site localized solely to the γ subunit has also been demonstrated. In contrast to the case with dicot thylakoids (spinach [Spinacia oleracea] and pea [Pisum sativum]) treatment of monocot thylakoids (maize, barley [Hordeum vulgare], crabgrass [Digitaria sanguinalis]) with bifunctional maleimides or thiol oxidants in the light does not result in functional uncoupling, i.e the bifunctional reagents act more like energy transfer inhibitors. The lack of functional uncoupling could be due either to a failure of the reagents to cross-link key sulfhydryl residues in the γ subunit or to the continued ability of the γ subunit to gate proton movements through the chloroplast coupling factor complex even though its conformation has been altered by sulfhydryl reagents.

Photosystem II Core Phosphorylation Heterogeneity, Differential Herbicide Binding, and Regulation of Electron Transfer in Photosystem II Preparations from Spinach 1

Giardi, Maria T.; Rigoni, Fernanda; Barbato, Roberto
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1992 EN
Relevância na Pesquisa
57.31831%
The effect of photosystem II core phosphorylation on the secondary quinone acceptor of photosystem II (QB) domain environment was analyzed by comparative herbicide-binding studies with photosystem II preparations from spinach (Spinacia oleracea L.). It was found that phosphorylation reduces the binding affinity for most photosynthetic herbicides. The binding of synthetic quinones and of the electron acceptor 2,6-dichlorophenolindophenol is also reduced by photosystem II phosphorylation. Four photosystem II core populations isolated from membranes showed different extents of phosphorylation as well as different degrees of affinity for photosynthetic herbicides. These findings support the idea that heterogeneity of photosystem II observed in vivo could be, in part, due to phosphorylation.

Short-Term Treatment with Cell Wall Degrading Enzymes Increases the Activity of the Inositol Phospholipid Kinases and the Vanadate-Sensitive ATPase of Carrot Cells 1

Chen, Qiuyun; Boss, Wendy F.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1990 EN
Relevância na Pesquisa
57.33362%
Treating carrot (Daucus carota L.) suspension culture cells with a mixture of cell wall degrading enzymes, Driselase, resulted in an increase in the percentage of [3H]phosphatidylinositol bisphosphate. Analysis of the lipid kinase activities in the isolated plasma membranes after whole cell treatment indicated that treatment with Driselase (2% weight/volume; the equivalent of 340 units per milliliter of hemicellulase and 400 units per milliliter of cellulase activity) or treatment with hemicellulase (31.7% weight/volume, 20.7 units per milliliter) resulted in an increase in the inositol phospholipid kinase activity. However, treatment with cellulase alone had no effect at 0.5% (weight/volume, 17.2 units per milliliter) or inhibited the kinase activity at 1% (weight/volume, 34.4 units per milliliter). The active stimulus in Driselase was heat sensitive. The plasma membrane vanadate-sensitive ATPase activity also increased when the cells were treated with Driselase. A time course study indicated that both the inositol phospholipid kinases and the plasma membrane vanadate-sensitive ATPase responded to as little as 5 seconds of treatment with 2% Driselase. However, at the lowest concentration of Driselase (0.04%, weight/volume) that resulted in an increase in inositol phospholipid kinase activity...

Analysis of Glucocerebrosides of Rye (Secale cereale L. cv Puma) Leaf and Plasma Membrane 1

Cahoon, Edgar B.; Lynch, Daniel V.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1991 EN
Relevância na Pesquisa
57.070034%
Glucocerebrosides of whole rye (Secale cerale L. cv Puma) leaf and plasma membrane were analyzed using gas chromatography-mass spectrometry and gas chromatography following hydrolysis or as intact molecules purified by reverse-phase high performance liquid chromatography. Fatty acids of acid-hydrolyzed leaf and plasma membrane glucocerebrosides consisted of >98 weight percent saturated and monounsaturated 2-hydroxy fatty acids which contained 16 to 26 carbon atoms. The major fatty acids detected were 2-hydroxynervonic acid (24:1h), 2-hydroxylignoceric acid (24:0h), 2-hydroxyerucic acid (22:1h), and 2-hydroxybehenic acid (22:0h). Long-chain bases of alkaline-hydrolyzed glucocerebrosides consisted primarily of cis-trans isomers of the trihydroxy base 4-hydroxysphingenine (t18:1) and the dihydroxy base sphingadienine (d18:2) with lesser amounts of 4-hydroxysphinganine (t18:0) and isomers of sphingenine (d18:1). Intact, underivatized glucocerebroside molecular species of rye leaf and plasma membrane were separated into more than 30 molecular species using reverse-phase HPLC. The molecular species composition of leaf and plasma membrane were quantitatively and qualitatively similar. The major molecular species was 24:1h-t18:1 which constituted nearly 40 weight percent of leaf and plasma membrane extracts. Several other species including 22:1h-t18:1...

Metabolically Driven Self-Restoration of Energy-Linked Functions by Avocado Mitochondria: General Characteristics and Phosphorylative Aspects

Huang, Li-Shar; Romani, Roger J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1991 EN
Relevância na Pesquisa
57.069224%
To assess the restorative capacity of isolated avocado (Persea americana) fruit mitochondria, the organelles were first aged in the absence of an energy source at 25°C for several hours until respiratory control and oxidative phosphorylation were greatly diminished or totally lost. Energy-linked functions were then gradually restored over a period of several hours after the addition of substrate. Restoration of respiratory control resulted from both an increase in state 3 and a decrease in state 4 respiratory rates. Either α-ketoglutarate or succinate served as restorants, each with distinctive rates of recovery in state 3 and state 4 respiration. ATP also served as a restorative agent but not as effectively as metabolizable substrate. ATP synthase activity was modulated by stress and restoration but neither the extent nor the rate of change was sufficient to constrain state 3 rates. Orthophosphate was released from the mitochondria during substrate-deprived stress. Restoration of phosphorylation preceded that of RC with phosphate uptake and phosphorylation being evident immediately upon the addition of substrate. During restoration [32P]orthophosphate was incorporated into several organic fractions: phospholipid, ATP, a trichloroacetic acid-precipitable mitochondrial fraction...

Biochemical Characteristics of Thylakoid Membranes in Chloroplasts of Dark-Grown Pine Cotyledons 1

Shinohara, Kenji; Murakami, Akio; Fujita, Yoshihiko
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1992 EN
Relevância na Pesquisa
57.33362%
Japanese black pine (Pinus thunbergii) cotyledons were found to synthesize chlorophylls in complete darkness during germination, although the synthesis was not as great as that in the light. The compositions of thylakoid components in plastids of cotyledons grown in the dark and light were compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of polypeptides and spectroscopic determination of membrane redox components. All thylakoid membrane proteins found in preparations from light-grown cotyledons were also present in preparations from dark-grown cotyledons. However, levels of photosystem I, photosystem II, cytochrome b[ill]/f, and light-harvesting chlorophyll-protein complexes in dark-grown cotyledons were only one-fourth of those in light-grown cotyledons, on a fresh weight basis. These results suggest that the low abundance of thylakoid components in dark-grown cotyledons is associated with the limited supply of chlorophyll needed to assemble the two photosystem complexes and the light-harvesting chlorophyll-protein complex.

Na+-Independent HCO3− Transport and Accumulation in the Cyanobacterium Synechococcus UTEX 625 1

Espie, George S.; Kandasamy, Ramani A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1992 EN
Relevância na Pesquisa
57.069224%
The active transport and intracellular accumulation of HCO3− by air-grown cells of the cyanobacterium Synechococcus UTEX 625 (PCC 6301) was strongly promoted by 25 millimolar Na+.Na+-dependent HCO3− accumulation also resulted in a characteristic enhancement in the rate of photosynthetic O2 evolution and CO2 fixation. However, when Synechococcus was grown in standing culture, high rates of HCO3− transport and photosynthesis were observed in the absence of added Na+. The internal HCO3− pool reached levels up to 50 millimolar, and an accumulation ratio as high as 970 was observed. Sodium enhanced HCO3− transport and accumulation in standing culture cells by about 25 to 30% compared with the five- to eightfold enhancement observed with air-grown cells. The ability of standing culture cells to utilize HCO3− from the medium in the absence of Na+ was lost within 16 hours after transfer to air-grown culture and was reacquired during subsequent growth in standing culture. Studies using a mass spectrometer indicated that standing culture cells were also capable of active CO2 transport involving a high-affinity transport system which was reversibly inhibited by H2S, as in the case for air-grown cells. The data are interpreted to indicate that Synechococcus possesses a constitutive CO2 transport system...

Comparative Kinetics and Reciprocal Inhibition of Nitrate and Nitrite Uptake in Roots of Uninduced and Induced Barley (Hordeum vulgare L.) Seedlings 1

Aslam, Muhammad; Travis, Robert L.; Huffaker, Ray C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1992 EN
Relevância na Pesquisa
57.07443%
Nitrate and NO2− transport by roots of 8-day-old uninduced and induced intact barley (Hordeum vulgare L. var CM 72) seedlings were compared to kinetic patterns, reciprocal inhibition of the transport systems, and the effect of the inhibitor, p-hydroxymercuribenzoate. Net uptake of NO3− and NO2− was measured by following the depletion of the ions from the uptake solutions. The roots of uninduced seedlings possessed a low concentration, saturable, low Km, possibly a constitutive uptake system, and a linear system for both NO3− and NO2−. The low Km system followed Michaelis-Menten kinetics and approached saturation between 40 and 100 micromolar, whereas the linear system was detected between 100 and 500 micromolar. In roots of induced seedlings, rates for both NO3− and NO2− uptake followed Michaelis-Menten kinetics and approached saturation at about 200 micromolar. In induced roots, two kinetically identifiable transport systems were resolved for each anion. At the lower substrate concentrations, less than 10 micromolar, the apparent low Kms of NO3− and NO2− uptake were 7 and 9 micromolar, respectively, and were similar to those of the low Km system in uninduced roots. At substrate concentrations between 10 and 200 micromolar...

Root Respiration Associated with Ammonium and Nitrate Absorption and Assimilation by Barley 1

Bloom, Arnold J.; Sukrapanna, Scott S.; Warner, Robert L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1992 EN
Relevância na Pesquisa
57.07075%
We examined nitrate assimilation and root gas fluxes in a wild-type barley (Hordeum vulgare L. cv Steptoe), a mutant (nar1a) deficient in NADH nitrate reductase, and a mutant (nar1a;nar7w) deficient in both NADH and NAD(P)H nitrate reductases. Estimates of in vivo nitrate assimilation from excised roots and whole plants indicated that the nar1a mutation influences assimilation only in the shoot and that exposure to NO3− induced shoot nitrate reduction more slowly than root nitrate reduction in all three genotypes. When plants that had been deprived of nitrogen for several days were exposed to ammonium, root carbon dioxide evolution and oxygen consumption increased markedly, but respiratory quotient—the ratio of carbon dioxide evolved to oxygen consumed—did not change. A shift from ammonium to nitrate nutrition stimulated root carbon dioxide evolution slightly and inhibited oxygen consumption in the wild type and nar1a mutant, but had negligible effects on root gas fluxes in the nar1a;nar7w mutant. These results indicate that, under NH4+ nutrition, 14% of root carbon catabolism is coupled to NH4+ absorption and assimilation and that, under NO3− nutrition, 5% of root carbon catabolism is coupled to NO3− absorption, 15% to NO3− assimilation...

Transport Interactions between Paraquat and Polyamines in Roots of Intact Maize Seedlings

Hart, Jonathan J.; DiTomaso, Joseph M.; Linscott, Dean L.; Kochian, Leon V.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1992 EN
Relevância na Pesquisa
57.069224%
Interactions between absorption of paraquat and the polyamines putrescine, cadaverine, and spermine in roots of intact maize (Zea mays L. cv 3377 Pioneer) seedlings were examined. Concentration-dependent kinetics for paraquat and putrescine influx were similar and both kinetic curves could be resolved into a linear and a saturable component. The linear component was previously shown to represent cell wall/membrane binding. The saturable components for paraquat and putrescine uptake, which represent influx across the plasmalemma, had Km values of 98 and 120 micromolar, respectively, and Vmax values of 445 and 456 nanomoles per gram fresh weight per hour, respectively. Lineweaver-Burk transformation of the saturable component of paraquat influx in the presence of varying concentrations of putrescine indicated that the diamine competitively inhibited the saturable component of paraquat uptake. Reciprocal experiments similarly demonstrated that paraquat competitively inhibited the saturable component of putrescine uptake. Competitive inhibition of both paraquat and putrescine influx could also be demonstrated with the diamine cadaverine, which has a charge distribution similar to that of paraquat and putrescine. In contrast, the larger...

Neomycin Inhibits the Phosphatidylinositol Monophosphate and Phosphatidylinositol Bisphosphate Stimulation of Plasma Membrane ATPase Activity 1

Chen, Qiuyun; Boss, Wendy F.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1991 EN
Relevância na Pesquisa
57.33808%
The inositol phospholipids, phosphatidylinositol monophosphate (PIP) and phosphatidylinositol bisphosphate (PIP2), have been shown to increase the vanadate-sensitive ATPase activity of plant plasma membranes (AR Memon, Q Chen, WF Boss [1989] Biochem Biophys Res Commun 162: 1295-1301). In this paper, we show the effect of various concentrations of phosphatidyinositol, PIP, and PIP2 on the plasma membrane vanadate-sensitive ATPase activity. PIP and PIP2 at concentrations of 10 nanomoles per 30 microgram membrane protein per milliliter of reaction mixture caused a twofold and 1.8-fold increase in the ATPase activity, respectively. The effect of these negatively charged phospholipids on the ATPase activity was inhibited by adding the positively charged aminoglycoside, neomycin. Neomycin did not affect the endogenous plasma membrane ATPase activity in the absence of exogenous lipids.

Partial Purification and Characterization of Three NAD(P)H Dehydrogenases from Beta vulgaris Mitochondria 1

Luethy, Michael H.; Hayes, Marianne K.; Elthon, Thomas E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1991 EN
Relevância na Pesquisa
57.070034%
Mitochondria isolated from the taproot of beet (Beta vulgaris) were used in an effort to identify and partially purify the proteins constituting the exogenous NADH dehydrogenase. Three NAD(P)H dehydrogenases are released from these mitochondria by sonication, and these enzymes were partially purified using fast protein liquid chromatography. One of the enzymes, designated peak I, is capable of oxidizing NADPH and the β form of NADH. The other two activities, peaks II and III, oxidize only β-NADH. All three peaks are insensitive to divalent cation chelators and a complex I inhibitor, rotenone. The major component to peak I is a polypeptide with an apparent molecular mass of approximately 42 kilodaltons. Peak I activity was insensitive to platanetin, a specific inhibitor of the exogenous dehydrogenase, and insensitive to added Ca2+ or Mg2+. Peak I displayed a broad pH activity profile with an optimum between 7.5 and 8.0 for both NADPH and NADH. Purified peak II gave a single polypeptide of about 32 kilodaltons, had a pH optimum between 7.0 and 7.5, and was slightly stimulated by Ca2+ and Mg2+. As with peak I, platanetin had no effect on peak II activity. Peak III was not purified completely, but contained two major polypeptides with apparent molecular masses of 55 and 40 kilodaltons. This enzyme was not affected by Ca2+ and Mg2+...

Calcium-Pumping ATPases in Vesicles from Carrot Cells 1: Stimulation by Calmodulin or Phosphatidylserine, and Formation of a 120 Kilodalton Phosphoenzyme

Hsieh, Wen-Ling; Pierce, Wayne S.; Sze, Heven
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1991 EN
Relevância na Pesquisa
57.327437%
Ca2+-ATPases keep cytoplasmic [Ca2+] low by pumping Ca2+ into intracellular compartments or out of the cell. The transport properties of Ca2+-pumping ATPases from carrot (Daucus carota cv Danvers) tissue culture cells were studied. ATP-dependent Ca2+ transport in vesicles that comigrated with an endoplasmic reticulum marker, was stimulated three- to fourfold by calmodulin. Cyclopiazonic acid (a specific inhibitor of the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase) partially inhibited oxalate-stimulated Ca2+ transport activity; however, it had no effect on calmodulin-stimulated Ca2+ uptake driven by ATP or GTP. The results would suggest the presence of two types of Ca2+-ATPases, an endoplasmic reticulum- and a plasma membrane-type. Interestingly, incubation of membranes with [gamma32P]ATP resulted in the formation of a single acyl [32P]phosphoprotein of 120 kilodaltons. Formation of this phosphoprotein was dependent on Ca2+, but independent of Mg2+. Its enhancement by La3+ is characteristic of a phosphorylated enzyme intermediate of a plasma membrane-type Ca-ATPase. Calmodulin stimulated Ca2+ transport was decreased by W-7 (a calmodulin antagonist), ML-7 (myosin light chain kinase inhibitor) or thyroxine. Acidic phospholipids, like phosphatidylserine...

Hormone Action on Transmembrane Electron and H+ Transport 1

Böttger, Michael; Hilgendorf, Frank
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1988 EN
Relevância na Pesquisa
57.07075%
A possible involvement of two different systems in proton translocation was investigated by simultaneous measurement of transmembrane electron flow and proton secretion in a pH-stat combined with a redoxstat. The pH gradient between cytoplasm and apoplast is probably maintained by an H+ -pumping ATPase and by a second proton extrusion system, which seems to be linked to a redox chain with NAD(P)H as electron donor. Indole acetic acid inhibits both e− and H+ efflux, but only if the `electron draw' from the outside is not too high. The electron draw depends on the hexacyanoferrate level at the plasmalemma surface and on the Ca2+ concentration. The inhibiting effect of auxin on e− and H+ efflux in the presence of hexacyanoferrate can be only detected at low levels of bivalent cations and of the artificial electron acceptor. The inhibition of e− and H+ efflux by auxin requires high oxygen levels. The influence of auxin on both e− and H+ transfer disappears below 2 kilopascals O2, a level which does not influence respiration. Ethanol and fusicoccin do not increase the e− flux, probably because the electron transfer from the plasma membrane to HCF III is the limiting step. If electron transfer is reduced by IAA pretreatment, ethanol increases e− flux. Fusicoccin decreases e− and increases H+ efflux if the rates have been lowered previously by indole acetic acid pretreatment. This effect depends on high oxygen levels and is reversible by lowering oxygen pressure. Auxin and Ca2+ change e− flow and H+ ejection in a 1:1 ratio.