15 research outputs found
Changes induced by malathion, methylparathion and parathion on membrane lipid physicochemical properties correlate with their toxicity
Perturbations induced by malathion, methylparathion and parathion on the physicochemical properties of dipalmitoylphosphatidylcholine (DPPC) were studied by fluorescence anisotropy of DPH and DPH-PA and by differential scanning calorimetry (DSC). Methylparathion and parathion (50 [mu]M) increased the fluorescence anisotropy evaluated by DPH-PA and DPH, either in gel or in the fluid phase of DPPC bilayers, but mainly in the fluid phase. Parathion is more effective than methylparathion. On the other hand, malathion had almost no effect. All the three xenobiotics displaced the phase transition midpoint to lower temperature values and broadened the phase transition profile of DPPC, the effectiveness following the sequence: parathion>methylparathion>>malathion. A shifting and broadening of the phase transition was also observed by DSC. Furthermore, at methylparathion/lipid molar ratio of 1/2 and at parathion/lipid molar ratio of 1/7, the DSC thermograms displayed a shoulder in the main peak, in the low temperature side, suggesting coexistence of phases. For higher ratios, the phase transition profile becomes sharp as the control transition, but the midpoint is shifted to the previous shoulder position. Conversely to methylparathion and parathion, malathion did not promote phase separation. The overall data from fluorescence anisotropy and calorimetry indicate that the degree of effect of the insecticides on the physicochemical membrane properties correlates with toxicity to mammals. Therefore, the in vivo effects of organophosphorus compounds may be in part related with their ability to perturb the phospholipid bilayer structure, whose integrity is essential for normal cell function.http://www.sciencedirect.com/science/article/B6T1T-42NY32W-K/1/9c5c8320a8dff42bbf122281b5056b8
Size dependence of the translational diffusion of large integral membrane proteins in liquid-crystalline phase lipid bilayers. A study using fluorescence recovery after photobleaching
The translational diffusion of bovine rhodopsin,
the Caz+-activated adenosinetriphosphatase of rabbit muscle
sarcoplasmic reticulum, and the acetylcholine receptor monomer
of Torpedo marmorata has been examined at a high
dilution (molar ratios of lipid/protein 1 3000/1) in liquidcrystalline
phase phospholipid bilayer membranes by using the
fluorescence recovery after photobleaching technique. These
integral membrane proteins having molecular weights of about
37 000 for rhodopsin, about 100000 for the adenosinetriphosphatase,
and about 250 000 for the acetylcholine receptor
were reconstituted into membranes of dimyristoylphosphatidylcholine
(rhodopsin and acetylcholine receptor),
soybean lipids (acetylcholine receptor), and a total lipid extract
of rabbit muscle sarcoplasmic reticulum (adenosinetriphosphatase).
The translational diffusion coefficients of all
the proteins at 310 K were found to be in the range (1-3) X
cm2/s. In consideration of the sizes of the membranebound
portions of these proteins, this result is in agreement
with the weak dependence of the translational diffusion
coefficient upon diffusing particle size predicted by continuum
fluid hydrodynamic models for the diffusion in membranes
[Saffman, P. G., & Delbriick, M. (1975) Proc. Natl. Acad.
Sci. U.S.A. 72, 3 1 1 1-3 1 131. Lipid diffusion was also examined
in the same lipid bilayers with the fluorescent lipid derivative
N-(7-nitro-2,1,3-benzoxadiazol-4-yl)dimyristoylphosphatidylethanolamine.
The translational diffusion coefficient
for this lipid derivative was found to be in the range
(9-14) X cm2/s at 310 K. In consideration of the dimensions
of the lipid molecule, this value for the lipid diffusion
coefficient is in agreement with the continuum fluid hydrodynamic
model only if a near-complete slip boundary condition
is assumed at the bilayer midplane. Alternatively, kinetic
diffusion models [Trauble, H., & Sackmann, E. (1972) J. Am.
Chem. SOC9. 4,4499-45101 may have to be invoked to explain
the lipid diffusion behavior
Lipid composition and dynamics of cell membranes of Bacillus stearothermophilus adapted to amiodarone
Bacillus stearothermophilus, a useful model to evaluate membrane interactions of lipophilic drugs, adapts to the presence of amiodarone in the growth medium. Drug concentrations in the range of 1-2 [mu]M depress growth and 3 [mu]M completely suppresses growth. Adaptation to the presence of amiodarone is reflected in lipid composition changes either in the phospholipid classes or in the acyl chain moieties. Significant changes are observed at 2 [mu]M and expressed by a decrease of phosphatidylethanolamine (relative decrease of 23.3%) and phosphatidylglycerol (17.9%) and by the increase of phosphoglycolipid (162%). The changes in phospholipid acyl chains are expressed by a decrease of straight-chain saturated fatty acids (relative decrease of 12.2%) and anteiso-acids (22%) with a parallel increase of the iso-acids (9.8%). Consequently, the ratio straight-chain/branched iso-chain fatty acids decreases from 0.38 (control cultures) to 0.30 (cultures adapted to 2 [mu]M amiodarone). The physical consequences of the lipid composition changes induced by the drug were studied by fluorescence polarization of diphenylhexatriene and diphenylhexatriene-propionic acid, and by differential scanning calorimetry. The thermotropic profiles of polar lipid dispersions of amiodarone-adapted cells are more similar to control cultures (without amiodarone) than those resulting from a direct interaction of the drug with lipids, i.e., when amiodarone was added directly to liposome suspensions. It is suggested that lipid composition changes promoted by amiodarone occur as adaptations to drug tolerance, providing the membrane with physico-chemical properties compatible with membrane function, counteracting the effects of the drug.http://www.sciencedirect.com/science/article/B6VNN-419BF60-K/1/8f2d4fae7f9c131d26230cf4123da94
Degradability and Sediment Sorption of an Alcohol Polyglycol Ether Surfactant Putatively Useful for the Control of Red Swamp Crayfish in Rice Fields
This work reports studies of the degradation rates of a fattyalcohol polyglycol ether non-ionic surfactant, Genapol OXD-080, putatively useful for the control of red swamp crayfish (Procambarus clarkii Girard) in rice fields under laboratory and field conditions. The influence of temperature,sediment site specificity and sorption were taken into account.The degradation kinetics of the surfactant depends on the experimental conditions: type of inocula and temperature. Thedistribution of this chemical in aquatic systems was also examined. Genapol OXD-080 was removed into the sedimentsreadily after application, and sorption was considered the majorpath of removal from the water phase. Data suggest that furtherstudies are required regarding the effects of Genapol OXD-080 in aquatic organisms resident in rice fields, in parallelwith the development of technologies related with the use ofsurfactants to control P. clarkii populations
Ethylazinphos Interaction with Membrane Lipid Organization Induces Increase of Proton Permeability and Impairment of Mitochondrial Bioenergetic Functions
Ethylazinphos increases the passive proton permeability of lipid bilayers reconstituted with dipalmitoylphosphatidylcholine (DPPC) and mitochondrial lipids. A sharp increase of proton permeability is detected at insecticide/lipid molar ratios identical to those inducing phase separation in the plane of DPPC bilayers, as revealed by differential scanning calorimetry (DSC). Ethylazinphos progressively depresses the transmembrane potential ([Delta][Psi]) of mitochondria supported by piruvate/malate, succinate, or ascorbate/TMPD. Additionally, a decreased depolarization induced by ADP depends on ethylazinphos concentration, reflecting a phosphorylation depression. This loss of phosphorylation is a consequence of a decreased [Delta][Psi]. A decreased respiratory control ratio is also observed, since ethylazinphos stimulates state 4 respiration and inhibits ADP-stimulated respiration (state 3). Ethylazinphos concentrations up to 100 nmol/mg mitochondrial protein increase the rate of state 4 together with a decrease in [Delta][Psi], without significant perturbation of state 3 and carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP)-uncoupled respiration. For increased insecticide concentrations, the state 3 and FCCP-uncoupled respiration are inhibited to approximately the same extent. The perturbations are more pronounced when the energization is supported by pyruvate/malate and less effective when succinate is used as substrate. The present data, in association with previous DSC studies, indicate that ethylazinphos, at concentrations up to 100 nmol/mg mitochondrial protein, interacts with the lipid bilayer of mitochondrial membrane, changing the lipid organization and increasing the proton permeability of the inner membrane. The increased proton permeability explains the decreased oxidative phosphorylation coupling. Resulting disturbed ATP synthesis may significantly underlie the mechanisms of ethylazinphos toxicity, since most of cell energy in eukaryotes is provided by mitochondria.http://www.sciencedirect.com/science/article/B6WXH-45BBYFP-25/1/8df8835c5305825c596440b25248b30
Ethylazinphos Interaction with Membrane Lipid Organization Induces Increase of Proton Permeability and Impairment of Mitochondrial Bioenergetic Functions
Ethylazinphos increases the passive proton permeability of lipid bilayers reconstituted with dipalmitoylphosphatidylcholine (DPPC) and mitochondrial lipids. A sharp increase of proton permeability is detected at insecticide/lipid molar ratios identical to those inducing phase separation in the plane of DPPC bilayers, as revealed by differential scanning calorimetry (DSC). Ethylazinphos progressively depresses the transmembrane potential ([Delta][Psi]) of mitochondria supported by piruvate/malate, succinate, or ascorbate/TMPD. Additionally, a decreased depolarization induced by ADP depends on ethylazinphos concentration, reflecting a phosphorylation depression. This loss of phosphorylation is a consequence of a decreased [Delta][Psi]. A decreased respiratory control ratio is also observed, since ethylazinphos stimulates state 4 respiration and inhibits ADP-stimulated respiration (state 3). Ethylazinphos concentrations up to 100 nmol/mg mitochondrial protein increase the rate of state 4 together with a decrease in [Delta][Psi], without significant perturbation of state 3 and carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP)-uncoupled respiration. For increased insecticide concentrations, the state 3 and FCCP-uncoupled respiration are inhibited to approximately the same extent. The perturbations are more pronounced when the energization is supported by pyruvate/malate and less effective when succinate is used as substrate. The present data, in association with previous DSC studies, indicate that ethylazinphos, at concentrations up to 100 nmol/mg mitochondrial protein, interacts with the lipid bilayer of mitochondrial membrane, changing the lipid organization and increasing the proton permeability of the inner membrane. The increased proton permeability explains the decreased oxidative phosphorylation coupling. Resulting disturbed ATP synthesis may significantly underlie the mechanisms of ethylazinphos toxicity, since most of cell energy in eukaryotes is provided by mitochondria.http://www.sciencedirect.com/science/article/B6WXH-45BBYFP-25/1/8df8835c5305825c596440b25248b30
Regulation by Magnesium of Potato Tuber Mitochondrial Respiratory Activities
Dehydrogenase activities of potato tuber mitochondria and corresponding phosphorylation rates were measured for the dependence on external and mitochondrial matrix Mg2+. Magnesium stimulated state 3 and state 4 respiration, with significantly different concentrations of matrix Mg2+ required for optimal activities of the several substrates. Maximal stimulation of respiration with all substrates was obtained at 2-mM external Mg2+. However, respiration of malate, citrate, and a-ketoglutarate requires at least 4-mM Mg2+ inside mitochondria for maximization of dehydrogenase activities. The phosphorylation system, requires a low level of internal Mg2+ (0.25 mM) to reach high activity, as judged by succinate-dependent respiration. However, mitochondria respiring on citrate or a-ketoglutarate only sustain high levels of phosphorylation with at least 4-mM matrix Mg2+. Respiration of succinate is active without external and matrix Mg2+, although stimulated by the cation. Respiration of a-ketoglutarate was strictly dependent on external Mg2+ required for substrate transport into mitochondria, and internal Mg2+ is required for dehydrogenase activity. Respiration of citrate and malate also depend on internal Mg2+ but, unlike a-ketoglutarate, some activity still remains without external Mg2+. All the substrates revealed insensitive to external and internal mitochondrial Ca2+, except the exogenous NADH dehydrogenase, which requires either external Ca2+ or Mg2+ for detectable activity. Calcium is more efficient than Mg2+, both having cumulative stimulation. Unlike Ca2+, Mn2+ could substitute for Mg2+, before and after addition of A23, showing its ability to regulate phosphorylation and succinate dehydrogenase activities, with almost the same efficiency as Mg2+
Fluidity of sarcoplasmic reticulum membranes investigated with dipyrenylpropane, an intramolecular excimer probe
Intramolecular excimer formation with 1,3-di( 1 -
pyreny1)propane was used to probe the fluidity of sarcoplasmic
reticulum (SR) membranes where the probe could be incorporated
(in a probe/lipid molar ratio of 1/2OOO or less) without
inducing any detectable damage. The temperature was varied
between -1 and 40 'C. The fluidity of the native SR membrane
changes from 52 CP at 40 OC to 325 CP at 5 'C. The
native SR membranes are less fluid than liposomes prepared
from total membrane lipids. The fluidity of membranes reconstituted
from the SR ATPase and a total lipid extract of the SR depends on the lipid/protein molar ratio and sharply
decreases when this ratio becomes lower than 44, for all temperatures
studied. This is in accord with literature reports
describing the Occurrence of approximately 30 lipid molecules
around the Ca-ATPase molecule in the SR membrane. Arrhenius
plots of the excimer to monomer fluorescence intensity
ratio in native and reconstituted SR membranes display a
break at about 20 OC which is not observed when the lipid/
protein ratio is lower than 44. This break is interpreted as
being a characteristic of the lipid portion of the membrane
Occurrence of Plant-Uncoupling Mitochondrial Protein (PUMP) in Diverse Organs and Tissues of Several Plants
The presence of plant-uncoupling mitochondrial protein (PUMP), previously described by Vercesi et al. (1995), was screened in mitochondria of various organs or tissues of several plant species. This was done functionally, by monitoring purine nucleotide-sensitive linoleic acid-induced uncoupling, or by Western blots. The following findings were established: (1) PUMP was found in most of the higher plants tested; (2) since ATP inhibition of linoleic acid-induced membrane potential decrease varied, PUMP content might differ in different plant tissues, as observed with mitochondria from maize roots, maize seeds, spinach leaves, wheat shoots, carrot roots, cauliflower, broccoli, maize shoots, turnip root, and potato calli. Western blots also indicated PUMP presence in oat shoots, carnation petals, onion bulbs, red beet root, green cabbage, and Sedum leaves. (3) PUMP was not detected in mushrooms. We conclude that PUMP is likely present in the mitochondria of organs and tissues of all higher plants
Modulation of sarcoplasmic reticulum calcium pump activity by membrane fluidity
Intramolecular excimerization of 1,3-di- l-pyrenylpropane
[Py(3)Py] was used to assess the fluidity of sarcoplasmic
reticulum membranes (SR); on the basis of the
spectral data, the probe incorporates completely inside the
membrane probably somewhere close to the polar head groups
of phospholipid molecules, however not in the very hydrophobic
core. The excimerization rate is very sensitive to lipid phase
transitions, as revealed by thermal profiles of dimyristoylphosphatidylcholine
(DMPC) and dipalmitoylphosphatidylcholine
(DPPC) bilayers. Cholesterol abolishes pretransitions
and broadens the thermal profiles of the main transitions which
vanish completely at 50 mol % sterol. Excimer formation in
liposomes of SR total lipid extracts does not show any sharp
transitions, as in the case of DMPC and DPPC. However,
the plots display discontinuities at about 20 OC which are
broadened by cholesterol and not observed at 50 mol % sterol. Also cholesterol has been incorporated in native SR membranes
by an exchange technique allowing progressive enrichment
without changing the phospholipid/protein molar
ratio. As in liposomes, discontinuities of excimer formation
at 20 OC are broadened by cholesterol enrichment. The full
activity of uncoupled Ca*+-ATPase is only affected by cholesterol
above a molar ratio to phospholipid of 0.4. However,
a significant decrease in activity (about 20%) is only noticed
at a ratio of 0.6 (the highest technically achieved); at this ratio,
about 28 lipid molecules per CaZ+-ATPase are expected to be
relatively free from cholesterol interaction. The vesicle
structure is still intact at this high ratio, as judged from the
absence of basal activity (not Ca2+ stimulated). However, the
sterol significantly decreases to about 60% the energetic efficiency
of Ca2+ pumping (CaZ+/ATP ratio)