Página 17 dos resultados de 686 itens digitais encontrados em 0.011 segundos

Rapeseed oil-rich diet alters in vitro menadione and nimesulide hepatic mitochondrial toxicity

Monteiro, João P.; Silva, Ana M.; Jurado, Amália S.; Oliveira, Paulo J.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
47.33362%
Diet-induced changes in the lipid composition of mitochondrial membranes have been shown to influence physiological processes. However, the modulation effect of diet on mitochondrially-active drugs has not yet received the deserved attention. Our hypothesis is that modulation of membrane dynamics by diet impacts drug-effects on liver mitochondrial functioning. In a previous work, we have shown that a diet rich in rapeseed oil altered mitochondrial membrane composition and bioenergetics in Wistar rats. In the present work, we investigated the influence of the modified diet on hepatic mitochondrial activity of two drugs, menadione and nimesulide, and FCCP, a classic protonophore, was used for comparison. The results showed that the effects of menadione and nimesulide were less severe on liver mitochondria for rats fed the modified diet than on rats fed the control diet. A specific effect on complex I seemed to be involved in drug-induced mitochondria dysfunction. Liver mitochondria from the modified diet group were more susceptible to nimesulide effects on MPT induction. The present work demonstrates that diet manipulation aimed at modifying mitochondrial membrane properties alters the toxicity of mitochondria active agents. This work highlights that diet may potentiate mitochondrial pharmacologic effects or increase drug-induced liabilities.

Studies on Octylphenoxy Surfactants 1: III. Sorption of Triton X-100 by Isolated Tomato Fruit Cuticles

Shafer, Warren E.; Bukovac, Martin J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1987 EN
Relevância na Pesquisa
47.344097%
Sorption characteristics of a polyethoxy (EO) derivative of octylphenol (OP) were determined for enzymically isolated mature tomato (Lycopersicon esculentum Mill. cv Sprinter) fruit cuticles at 25°C. Sorption was followed using 14C-labeled OP + 9.5EO (Triton X-100). Solution pH (2.2-6.2) did not affect surfactant sorption by tomato fruit cuticular membranes (CM). Surfactant concentration (0.001-1.0%, w/v) had a marked impact on sorption. Sorption equilibrium was reached in 24 hours for OP + 9.5EO concentrations below the critical micelle concentration (CMC), whereas 72 to 120 hours were required to reach equilibrium with concentrations greater than the CMC. Regardless of when equilibrium was attained, initial sorption of OP + 9.5EO occurred rapidly. Partition coefficients (K) of approximately 300 were obtained at pre-CMC concentrations, whereas at the highest concentration (1.0%), K values were approximately 15- to 20-fold lower. Sorption was higher for dewaxed CM (DCM) than for CM. At OP + 9.5EO concentrations below the CMC, the amount (millimoles per kilogram) sorbed by CM and DCM increased sharply as the CMC was reached. After an apparent plateau in the amount sorbed at concentrations immediately below and above the CMC, sorption by CM and DCM increased dramatically with OP + 9.5EO concentrations greater than the CMC (0.5 and 1.0%). In contrast...

Rapid Changes in Plasma Membrane Protein Phosphorylation during Initiation of Cell Wall Digestion 1

Blowers, David P.; Boss, Wendy F.; Trewavas, Anthony J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1988 EN
Relevância na Pesquisa
47.33362%
Plasma membrane vesicles from wild carrot cells grown in suspension culture were isolated by aqueous two-phase partitioning, and ATP-dependent phosphorylation was measured with [γ-32P]ATP in the presence and absence of calcium. Treatment of the carrot cells with the cell wall digestion enzymes, driselase, in a sorbitol osmoticum for 1.5 min altered the protein phosphorylation pattern compared to that of cells treated with sorbitol alone. Driselase treatment resulted in decreased phosphorylation of a band of Mr 80,000 which showed almost complete calcium dependence in the osmoticum treated cells; decreased phosphorylation of a band of Mr 15,000 which showed little calcium activation, and appearance of a new band of calcium-dependent phosphorylation at Mr 22,000. These effects appeared not to be due to nonspecific protease activity and neither in vivo nor in vitro exposure to driselase caused a significant loss of Coomassie blue-staining bands on the gels of the isolated plasma membranes. However, protein phosphorylation was decreased. Adding driselase to the in vitro reaction mixture caused a general decrease in the membrane protein phosphorylation either in the presence or absence of calcium which did not mimic the in vivo response. Cells labeled in vivo with inorganic 32P also showed a response to the Driselase treatment. An enzymically active driselase preparation was required for the observed responses.

On the Presence of a Nicotinamide Nucleotide Transhydrogenase in Mitochondria from Potato Tuber 1

Carlenor, E.; Persson, B.; Glaser, E.; Andersson, B.; Rydström, J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1988 EN
Relevância na Pesquisa
47.341455%
Mitochondria isolated from potato (Solanum tuberosum L.) tuber were investigated for the presence of a nicotinamide nucleotide transhydrogenase activity. Submitochondrial particles derived from these mitochondria by sonication catalyzed a reduction of NAD+ or 3-acetylpyridine-NAD+ by NADPH, which showed a maximum of about 50 to 150 nanomoles/minute·milligram protein at pH 5 to 6. The Km values for 3-acetylpyridine-NAD+ and NADPH were about 24 and 55 micromolar, respectively. Intact mitochondria showed a negligible activity in the absence of detergents. However, in the presence of detergents the specific activity approached about 30% of that seen with submitochondrial particles. The potato mitochondria transhydrogenase activity was sensitive to trypsin and phenylarsine oxide, both agents that are known to inhibit the mammalian transhydrogenase. Antibodies raised against rat liver transhydrogenase crossreacted with two peptides in potato tuber mitochondrial membranes with a molecular mass of 100 to 115 kilodaltons. The observed transhydrogenase activities may be due to an unspecific activity of dehydrogenases and/or to a genuine transhydrogenase. The activity contributions by NADH dehydrogenases and transhydrogenase to the total transhydrogenase activity were investigated by determining their relative sensitivities to trypsin. It is concluded that...

Ferredoxin Cross-Links to a 22 kD Subunit of Photosystem I 1

Zilber, April L.; Malkin, Richard
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1988 EN
Relevância na Pesquisa
47.33808%
We have used a cross-linking approach to study the interaction of ferredoxin (Fd) with photosystem I (PSI). The cross-linking reagent N-ethyl-3-(3-dimethylaminopropyl) carbodiimide was found to cross-link spinach Fd to a 22 kilodalton subunit of PSI in both isolated spinach (Spinacia oleracea) PSI complexes and spinach thylakoid membranes. The product had an apparent molecular weight of 38 kilodaltons on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and was identified as a cross-linked product using specific antibodies to Fd and the 22 kilodalton subunit. In both a native PSI complex (200 Chl/P700) and a PSI core complex (100 Chl/P700), a second cross-linked product at 36 kilodaltons was seen. The latter cross-reacted with an antibody to Fd but did not cross-react with antibodies directed against the 24.3, 22, 19, 17.3 or 8.5 kilodalton, or psaC subunits of PSI. Its composition remains to be determined. In thylakoids only the 38 kilodalton product was observed along with a cross-linked complex of Fd and Fd:NADP+ reductase.

Structural Aspects of Photosystem I from Dunaliella salina1

Bruce, Barry D.; Malkin, Richard
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1988 EN
Relevância na Pesquisa
47.33362%
A native PSI complex and a PSI core complex have been isolated from the halophilic green alga, Dunaliella salina. The composition and properties of these complexes are similar to previously described PSI complexes from spinach membranes. By growth on 14C-NaHCO3, it has been possible to isolate uniformly labeled 14C-PSI complexes in order to determine PSI subunit stoichiometry. This analysis has shown a ratio of one copy of three low molecular weight subunits (22,000; 15,000; 8,000) per two copies of high molecular weight subunits (84,000). Using a 14C-labeled cytochrome b6-f complex as an internal protein standard, it has been possible to estimate the molecular weight of a PSI core complex as about 330,000. This complex contains one P700, two 84,000 subunits, and one subunit of 22,000, 15,000, and 8,000.

Chloroplast Thylakoid Protein Phosphatase Is a Membrane Surface-Associated Activity 1

Sun, Gongqin; Bailey, Doreen; Jones, Michael W.; Markwell, John
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1989 EN
Relevância na Pesquisa
47.33362%
Chloroplast thylakoid protein phosphatase activity was measured using 32P-labeled histone as an exogenous substrate and an assay of the 32Pi released involving formation of a phosphomolybdate complex and organic extraction. The activity was liberated from wheat (Triticum aestivum) thylakoids by washing the membranes in NaCl-containing solutions followed by centrifugation. The liberated phosphatase activity had a pH optimum of approximately 6.75, was inhibited by addition of 10 millimolar EDTA or EGTA, and was stimulated by addition of millimolar amounts of dithiothreitol, magnesium, manganese, or calcium ions. The rate of thylakoid protein dephosphorylation was decreased following liberation of a portion of the protein phosphatase activity and was increased by addition of salt-liberated phosphatase fraction. These results suggest that at least a portion of wheat thylakoid protein phosphatase is a peripheral, rather than an integral, membrane protein.

Effect of Inhibition of Glycosylation on the Appearance of a 60 kD Membrane Glycopolypeptide in Endomembrane Fractions of Soybean Root

LaFayette, Peter R.; Travis, Robert L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1989 EN
Relevância na Pesquisa
47.341455%
Endomembrane (endoplasmic reticulum, Golgi apparatus, plasma membrane) proteins of soybean (Glycine max) root cells are highly glycosylated. We investigated whether N-linked oligosaccharide moieties are essential for the correct intracellular transport of plant endomembrane glycoproteins. Excised roots were incubated with tunicamycin, to block cotranslational glycosylation of proteins, and dual labeled with [3H]glucosamine and [35S] (methionine, cysteine). In the presence of tunicamycin, the incorporation of glucosamine into membrane proteins was inhibited by 60 to 90% while amino acid incorporation was only slightly affected. Autoradiograms of two-dimensionally separated polypeptides from each endomembrane fraction revealed the presence of at least one new polypeptide in tunicamycin-treated tissue. The new polypeptide was of the same isoelectric point but lower molecular weight than a preexisting polypeptide. The new polypeptide was unreactive to concanavalin A, as opposed to the preexisting polypeptide, suggesting the absence of the glycan portion. Trifluoromethanesulfonic acid and N-glycanase were used to cleave the carbohydrate from the preexisting concanavalin A binding polypeptide. In each case a deglycosylated polypeptide of the same isoelectric point and molecular weight as the new polypeptide from tunicamycin-treated tissue resulted. Since the absence of carbohydrate from the new endomembrane polypeptide did not prevent its appearance on autoradiograms of Golgi and plasma membrane...

Electrophoretic Characterization of a Detergent-Treated Plasma Membrane Fraction from Corn Roots 1

Gallagher, Sean R.; Leonard, Robert T.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1987 EN
Relevância na Pesquisa
47.341455%
Experiments were conducted to determine conditions essential for electrophoretic characterization of a detergent-extracted plasma membrane fraction from corn (Zea mays L.) roots. Sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) initially gave poor resolution of polypeptides in the plasma membrane fraction and, upon detergent treatment for purification of the proton-pumping adenosine triphosphatase (ATPase), showed no enrichment for a 100 kilodalton catalytic subunit characteristic of the ATPase. In contrast to SDS-PAGE, phenol urea acetic acid (PAU)-PAGE clearly resolved two polypeptides in the 100 kilodalton region that were enriched during detergent treatment and indicated at least one polypeptide forms a phosphorylated intermediate characteristic of the ATPase. Problems with SDS-PAGE were found to be caused, in part, by a combination of endogenous proteases and heat-induced aggregation of high molecular weight proteins. The usually standard procedure of boiling the sample prior to SDS-PAGE caused the aggregation of the 100 kilodalton polypeptides. By controlling for proteases using chymostatin and/or phenylmethane sulfonyl floride, and not boiling the sample prior to electrophoresis, two polypeptides were clearly resolved by SDS-PAGE in the 100 kilodalton region of Triton X-114-extracted membranes from corn...

Proton Gradients in Intact Cyanobacteria 1

Belkin, Shimshon; Mehlhorn, Rolf J.; Packer, Lester
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1987 EN
Relevância na Pesquisa
47.344097%
The internal pH values of two unicellular cyanobacterial strains were determined with electron spin resonance probes, over an external pH range of 6 to 9, in the light and in the dark. The slow growing, thylakoid-lacking Gloeobacter violaceus was found to have a low capacity for maintaining a constant internal pH. The distribution pattern of weak acid and amine nitroxide spin probes across the cell membranes of this organism, in the light and in the dark, was consistent with the assumption that it contains a single intracellular compartment. At an external pH of 7.0, intracellular pH was 6.8 in the dark and 7.2 in the light. The cells of Agmenellum quadruplicatum, a marine species, were found to contain two separate compartments; in the dark, the pH of the cytoplasmic and the intrathylakoid spaces were calculated to be 7.2 and 5.5, respectively. Upon illumination, the former increased and the latter decreased by about 0.5 pH units.

Transmembrane Signaling via Phosphatidylinositol 4,5-Bisphosphate Hydrolysis in Plants 1

Einspahr, Kregg J.; Thompson, Guy A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1990 EN
Relevância na Pesquisa
47.341455%
Recent investigations have confirmed the presence of the polyphosphoinositides, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate (PIP2), as well as inositol phospholipid-specific phospholipase C in higher plant and microalgal cells. In addition, it has been shown that stimulation of some photosynthetic cell types by environmental or hormonal challenge is accompanied by degradation of the polyphosphoinositides. The products of phospholipase C-catalyzed PIP2 hydrolysis, inositol 1,4,5-trisphosphate and diacylglycerol, appear to be capable of releasing organelle-bound Ca2+ and stimulating protein kinase C-like activity in vitro. However, a direct cause and effect relationship between stimulated PIP2 breakdown and changes in intracellular calcium, protein phosphorylation, or cell function has not yet been unequivocally established. Despite a number of technical difficulties slowing progress in this field, it is likely that photosynthetic organisms will soon be shown to transmit physiologically significant extracellular signals across their plasma membranes by a PIP2-mediated transduction mechanism.

Photolabeling of Tonoplast from Sugar Beet Cell Suspensions by [3H]5-(N-Methyl-N-Isobutyl)-Amiloride, an Inhibitor of the Vacuolar Na+/H+ Antiport 1

Barkla, Bronwyn J.; Charuk, Jeffrey H. M.; Cragoe, Edward J.; Blumwald, Eduardo
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1990 EN
Relevância na Pesquisa
47.341455%
The effects of 5-(N-methyl-N-isobutyl)-amiloride (MIA), an amiloride analog, was tested on the Na+/H+ antiport activity of intact vacuoles and tonoplast vesicles isolated from sugar beet (Beta vulgaris L.) cell suspension cultures. MIA inhibited Na+/H+ exchange in a competitive manner with a Ki of 2.5 and 5.9 micromolar for ΔpH-dependent 22Na+ influx in tonoplast vesicles and Na+-dependent H+ efflux in intact vacuoles, respectively. Scatchard analysis of the binding of [3H]MIA to tonoplast membranes revealed a high affinity binding component with a Kd of 1.3 micromolar. The close relationship between the dissociation constant value obtained and the constants of inhibition for MIA obtained by fluorescence quenching and isotope exchange suggests that the high affinity component represents a class of sites associated with the tonoplast Na+/H+ antiport. Photolabeling of the tonoplast with [3H]MIA revealed two sets of polypeptides with a different affinity to amiloride and its analog.

Mechanism of the Decline in Vacuolar H+ -ATPase Activity in Mung Bean Hypocotyls during Chilling 1

Matsuura-Endo, Chie; Maeshima, Masayoshi; Yoshida, Shizuo
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1992 EN
Relevância na Pesquisa
47.33362%
The mechanism responsible for the decrease in the activity of vacuolar H+ -ATPase during chilling was investigated in seedlings of mung bean (Vigna radiata). After chilling at 0°C for 3 d, the activity of vacuolar H+ -ATPase, calculated on the basis of membrane protein, decreased to 47% of the original value. Of the nine subunits of the ATPase, the specific contents of at least six subunits, of 68, 57, 44, 38, 37, and 32 kD, decreased in vacuolar membranes after chilling, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These subunits were released by treatment with chaotropic anions such as thiocyanate. The level of the 16-kD subunit did not change. Immunoblot analyses showed the decrease in the levels of the subunits of 68, 57, and 32 kD. Furthermore, the specific activity of the ATPase purified from chilled hypocotyls was two-thirds of that of the enzyme from nonchilled seedlings, and the enzyme from chilled tissue retained only a small amount of the 32-kD subunit. These results suggest that a selective release of the peripheral subunits of the ATPase from the membrane and a partial degradation of the ATPase complex may occur in vivo during chilling.

Tonoplast-Bound Protein Kinase Phosphorylates Tonoplast Intrinsic Protein 1

Johnson, Kenneth D.; Chrispeels, Maarten J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1992 EN
Relevância na Pesquisa
47.33808%
Tonoplast intrinsic protein (TIP) is a member of a family of putative membrane channels found in bacteria, animals, and plants. Plants have seed-specific, vegetative/reproductive organ-specific, and water-stress-induced forms of TIP. Here, we report that the seed-specific TIP is a phosphoprotein whose phosphorylation can be monitored in vivo by allowing bean cotyledons to take up [32P]orthophosphate and in vitro by incubating purified tonoplasts with γ-labeled [32P]ATP. Characterization of the in vitro phosphorylation of TIP indicates that a membrane-bound protein kinase phosphorylates TIP in a Ca2+-dependent manner. The capacity of the isolated tonoplast membranes to phosphorylate TIP declined markedly during seed germination, and this decline occurred well before the development-mediated decrease in TIP occurs. Phosphoamino acid analysis of purified, radiolabeled TIP showed that serine is the major, if not only, phosphorylated residue, and cyanogen bromide cleavage yielded a single radioactive peptide peak on a reverse-phase high-performance liquid chromatogram. Estimation of the molecular mass of the cyanogen bromide phosphopeptide by laser desorption mass spectroscopy led to its identification as the hydrophilic N-terminal domain of TIP. The putative phosphate-accepting serine residue occurs in a consensus phosphorylation site for serine/threonine protein kinases.

Involvement of Singlet Oxygen in 5-Aminolevulinic Acid-Induced Photodynamic Damage of Cucumber (Cucumis sativus L.) Chloroplasts 1

Chakraborty, Niranjan; Tripathy, Baishnab Charan
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1992 EN
Relevância na Pesquisa
47.341455%
Cucumber (Cucumis sativus L., cv Poinsette) plants were sprayed with 20 millimolar 5-aminolevulinic acid and then incubated in the dark for 14 hours. The intact chloroplasts were isolated from the above plants in the dark and were exposed to weak light (250 micromoles per square meter per second). Within 30 minutes, photosystem II activity was reduced by 50%. The singlet oxygen (1O2) scavengers, histidine and sodium azide (NaN3) significantly protected against the damage caused to photosystem II. The hydroxyl radical scavenger formate failed to protect the thylakoid membranes. The production of 1O2 monitored as N,N-dimethyl p-nitrosoaniline bleaching increased as a function of light exposure time of treated chloroplasts and was abolished by the 1O2 quencher, NaN3. Membrane lipid peroxidation monitored as malondialdehyde production was also significantly reduced when chloroplasts were illuminated in the presence of NaN3 and histidine. Protochlorophyllide was the most abundant pigment accumulated in intact chloroplasts isolated from 5-aminolevulinic acid-treated plants and was probably acting as type II photosensitizer.

Selective Inhibition of Active Uptake of Sucrose into Plasma Membrane Vesicles by Polyclonal Sera Directed against a 42 Kilodalton Plasma Membrane Polypeptide 1

Gallet, Olivier; Lemoine, Rémi; Gaillard, Cécile; Larsson, Christer; Delrot, Serge
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1992 EN
Relevância na Pesquisa
47.33362%
Several polyclonal sera were raised in rabbits and in mice against putative sucrose carrier proteins, i.e. a 42 kilodalton (O Gallet, R Lemoine, C Larsson, S Delrot [1989] Biochim Biophys Acta 978: 56-64) and a 62 kD (KG Ripp, PV Viitanen, WD Hitz, VR Fransceschi [1988] Plant Physiol 88: 1435-1445) polypeptide of the plasma membrane. The effects of these sera on the active uptake of sucrose and of valine into purified plasma membrane vesicles from sugar beet (Beta vulgaris L.) leaves and roots were studied. At a dilution of 1/50, the anti-42 kilodalton sera consistently inhibited sucrose uptake in plasma membranes from leaves or from roots. They had no effect on valine uptake. Under the same experimental conditions, the anti-62 kilodalton sera had no effect on active uptake of sucrose. The data further support the view that a 42 kilodalton polypeptide is a component of the transport system mediating sucrose uptake across the plasma membrane of plant cells.

Plasma Membrane Ca-ATPase of Radish Seedlings 1: II. Regulation by Calmodulin

Rasi-Caldogno, Franca; Carnelli, Antonella; De Michelis, Maria I.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1992 EN
Relevância na Pesquisa
47.33808%
The effect of calmodulin on the activity of the plasma membrane Ca-ATPase was investigated on plasma membranes purified from radish (Raphanus sativus L.) seedlings. Calmodulin stimulated the hydrolytic activity and the transport activity of the plasma membrane Ca-ATPase to comparable extents in a manner dependent on the free Ca2+ concentration. Stimulation was marked at low, nonsaturating Ca2+ concentrations and decreased increasing Ca2+, so that the effect of calmodulin resulted in an increase of the apparent affinity of the enzyme for free Ca2+. The pattern of calmodulin stimulation of the plasma membrane Ca-ATPase activity was substantially the same at pH 6.9 and 7.5, in the presence of ATP or ITP, and when calmodulin from radish seeds was used rather than that from bovine brain. At pH 6.9 in the presence of 5 micromolar free Ca2+, stimulation of the plasma membrane Ca-ATPase was saturated by 30 to 50 micrograms per milliliter bovine brain calmodulin. The calmodulin antagonist calmidazolium inhibited both basal and calmodulin-stimulated plasma membrane Ca-ATPase activity to comparable extents.

The use of a potential-sensitive cyanine dye for studying ion-dependent electrogenic renal transport of organic solutes. Uptake of l-malate and d-malate by luminal-membrane vesicles

Kragh-Hansen, Ulrich; Jørgensen, Karl Evald; Sheikh, M. Iqbal
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/11/1982 EN
Relevância na Pesquisa
47.341455%
The mechanisms of uptake of dicarboxylic acids by rabbit renal luminal-membrane vesicles were studied by the use of filtration and spectrophotometric techniques as described in an accompanying paper [Kragh-Hansen, Jørgensen & Sheikh (1982) Biochem. J. 208, 359–368]. Addition of l- or d-malate to dye-membrane-vesicle suspensions in the presence of Na+ gradients (extravesicular>intravesicular) resulted in spectral curves indicative of depolarization events. The renal uptake of dicarboxylic acids was dependent on the type of Na+-salt anion present and could be correlated with the ability of the anions to penetrate biological membranes (i.e. Cl−>SO42−>gluconate). Identical results were obtained by a filtration technique with Sartorius membrane filters. The results indicate that the dicarboxylic acids are taken up by the membrane vesicles in an electrically positive form (i.e. Na+/substrate coupling ratio 3:1) by an Na+-dependent transport system. This proposal was further supported by spectrophotometric experiments with various ionophores such as valinomycin, gramicidin and nigericin. The absorbance changes associated with simultaneous addition of l- and d-malate and spectrophotometric competition studies revealed that the two isomers are taken up by a common transport system. Spectral changes of the dye induced by addition of increasing concentrations of l- or d-malate indicated that the transport system favours the unphysiological d-form rather than the l-form of malate. Furthermore...

The internal pH and membrane potential of the insulin-secretory granule

Hutton, John C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/04/1982 EN
Relevância na Pesquisa
47.34622%
The membrane potential (ΔΨ) and the pH gradient (ΔpH) across the membrane of the insulin-secretory granule were determined in studies in vitro from the uptake of the permeant anion thio[14C]cyanate or the permeant base [14C]methylamine. Freshly prepared granules incubated in iso-osmotic medium containing sucrose and low concentrations of buffer salts exhibited an acidic internal pH and a ΔΨ positive inside. Addition of MgATP2− under these conditions did not alter the ΔpH, but produced a marked increase in the ΔΨ. Conversely, when a permeant anion was also included, ATP produced a marked increase in the ΔpH and a lesser increment in the ΔΨ. NH4+ salts reduced the ΔpH across granule membranes. In the presence of ATP this effect was accompanied by a reciprocal increase in the ΔΨ. A similar reciprocity was evident when nigericin was added together with K+ or on decreasing the medium pH, suggesting that these gradients were linked by a common electrogenic process. The effects of ATP were reversed by the protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone, the combination of valinomycin, nigericin and K+, and by the Mg2+-dependent ATPase inhibitor tributyltin. Uptakes of 14C-labelled tracer molecules were also markedly reduced by cryogenic disruption of the granule membrane or hypo-osmotic incubation conditions. These results were readily interpreted within a chemiosmotic hypothesis...

Quality Control of Photosystem II: REACTIVE OXYGEN SPECIES ARE RESPONSIBLE FOR THE DAMAGE TO PHOTOSYSTEM II UNDER MODERATE HEAT STRESS*

Yamashita, Amu; Nijo, Nobuyoshi; Pospíšil, Pavel; Morita, Noriko; Takenaka, Daichi; Aminaka, Ryota; Yamamoto, Yoko; Yamamoto, Yasusi
Fonte: American Society for Biochemistry and Molecular Biology Publicador: American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
Publicado em 17/10/2008 EN
Relevância na Pesquisa
47.341455%
Moderate heat stress (40 °C for 30 min) on spinach thylakoid membranes induced cleavage of the reaction center-binding D1 protein of photosystem II, aggregation of the D1 protein with the neighboring polypeptides D2 and CP43, and release of three extrinsic proteins, PsbO, -P, and -Q. These heat-induced events were suppressed under anaerobic conditions or by the addition of sodium ascorbate, a general scavenger of reactive oxygen species. In accordance with this, singlet oxygen and hydroxyl radicals were detected in spinach photosystem II membranes incubated at 40 °C for 30 min with electron paramagnetic resonance spin-trapping spectroscopy. The moderate heat stress also induced significant lipid peroxidation under aerobic conditions. We suggest that the reactive oxygen species are generated by heat-induced inactivation of a water-oxidizing manganese complex and through lipid peroxidation. Although occurring in the dark, the damages caused by the moderate heat stress to photosystem II are quite similar to those induced by excessive illumination where reactive oxygen species are involved.