RESUMO
It is argued that the different modes of fracturing of the erythrocyte membrane and the outer membrane of Escherichia coli with respect to the intramembraneous particles have their definite biochemical and structural counterpart i.e.,. the non-complementary particles of the erythrocyte membrane being predominantly proteinaceous in nature and the complementary particles of the outer membrane of E. coli being determined by lipopolysaccharide. Evaluation of the complementarity aspect of intramembraneous particles shows than an assessment of complementarity in replicas may decisive when interpreting micrographs at the macromolecular level.
Assuntos
Membrana Celular/ultraestrutura , Membrana Eritrocítica/ultraestrutura , Eritrócitos/ultraestrutura , Escherichia coli/ultraestrutura , Técnica de Fratura por Congelamento/métodos , Humanos , Lipopolissacarídeos/análise , Proteínas de Membrana/análise , Microscopia Eletrônica/métodosRESUMO
1. The influence of Ca2+ on the polymorphic phase behaviour of cardiolipin has been investigated employing 31P NMR and freeze-fracture techniques. The close correlation between the results obtained here and previous X-ray studies (Rand, R.P. and Sengupta, S. (1972) Biochim. Biophys. Acta 255, 484--492) confirms 31P NMR as a useful analytical procedure for investigating the polymorphic phase behaviour of hydrated phospholipids. 2. Ca2+ induces formation of the hexagonal (H11) phase via an intermediary phase which is observed at Ca2+/cardiolipin ratios of less than 1 (mol/mol). This intermediary appears to consist of "inverted' structure which lies adjacent to regions of bilayer structure. 3. The local anaesthetics dibucaine and chlorpromazine produce similar phase changes for cardiolipin as does Ca2+. It is suggested that the anaesthetics interact with the membrane in their charged form and induce their effects by charge neutralization.
Assuntos
Cardiolipinas , Cálcio , Fenômenos Químicos , Físico-Química , Clorpromazina , Dibucaína , Ácido Edético , Técnica de Fratura por Congelamento , Lipossomos , Espectroscopia de Ressonância MagnéticaRESUMO
Freeze-fracture electron microscopy demonstrates that in photosynthetic membranes of the blue-green alga Anacystis nidulans quenched from a temperature below growth temperature, areas devoid of membrane particles occur. We suggest that this phenomenon is related to phase transitions in the photosynthetic membrane.
Assuntos
Membrana Celular/ultraestrutura , Cianobactérias/ultraestrutura , Fotossíntese , Técnica de Fratura por Congelamento , Microscopia EletrônicaAssuntos
Envelhecimento , Cristalino/ultraestrutura , Animais , Bovinos , Membrana Celular/metabolismo , Membrana Celular/ultraestrutura , Colesterol/metabolismo , Eletroforese em Gel de Poliacrilamida , Técnica de Fratura por Congelamento , Cristalino/embriologia , Cristalino/metabolismo , Lipídeos de Membrana/metabolismo , Proteínas de Membrana/metabolismo , Microscopia Eletrônica , Fosfolipídeos/metabolismoRESUMO
The size and population density of large and small particles from freeze-fractured chloroplasts of three wild-type algae and of normal spinach were determined. Computer analyses of low-temperature absorption spectra of chloroplast preparations from these species were performed, and a possible correlation between the occurrence of seven chlorophyll complexes and the aforementioned properties of the intramembranous particles was studies. It was found that only single-sized particles occur in a species containing neither chlorophyll b nor chlorophyll a-685 complexes. The three remaining species carry particles of two sizes, termed large and small particles. However, from quantitative considerations it is concluded that the chlorophyll content of none of the various pigment complexes is related to the size and the population density of the studied particles. If such a relationship exists, it seems likely to be due to the carrier moiety of the chorophyll b-chlorophyll a-685 complex.
Assuntos
Clorofila/metabolismo , Cloroplastos/metabolismo , Cloroplastos/ultraestrutura , Euglena gracilis/metabolismo , Eucariotos/metabolismo , Técnica de Fratura por Congelamento , Membranas/metabolismo , Membranas/ultraestrutura , Plantas , Especificidade da EspécieRESUMO
During cell division in the Xenopus egg (diameter 1.25 mm) new cell membrane is formed in the furrow region (rate of growth approx 4-10(4) mum2/min). Freeze-fracture electron microscopy has produced the following data. Preexisting plasma membrane faces show a reversed polarity with respect to particle distribution, i.e. more particles are attached to the E-face (density 1600-2200 particles/mum2) than to the P-face (300 particles/mum2). A frequency histogram of 2331 measured intramembranous particles does not show a continuous range of sizes. The following sizes were very obvious: 95 A (12%), 125 A (30%) and 180 A (6%). At the tips of surface protrusions both the E- and the P- face are particle-free. Nascent cell membrane fracture faces are more difficult to obtain. The particle density is low (E-face 300-500 particles/mum2). Lowering the ambient temperature to 5 degrees C for approx. 5 mins does not change the normal particle pattern, but it improves the output in nascent membrane fracture faces. The fact that in the Xenopus egg preexisting and nascent membrane regions are continuous but nevertheless maintain their highly different particle densities is noteworthy. The freeze-fracture data are discussed in relation to, among other things, the known values of the specific resistances of these membrane regions.
Assuntos
Divisão Celular , Membrana Celular/fisiologia , Óvulo/fisiologia , Animais , Divisão Celular/efeitos dos fármacos , Membrana Celular/efeitos dos fármacos , Membrana Celular/ultraestrutura , Citocalasinas/farmacologia , Feminino , Técnica de Fratura por Congelamento , Microscopia Eletrônica , Óvulo/efeitos dos fármacos , Óvulo/ultraestrutura , XenopusRESUMO
Adhesion followed by fusion of LP-X vesicles with the erythrocyte membrane is an important contribution to the erythrocyte enlargement in patients with intra or extra hepatic cholestasis. Adhesion of LP-X vesicles is demonstrated by thin section and freeze-etch electronmicroscopy. Fusion of LP-X with the erythrocyte membrane is deduced from biochemical data and freeze-etch electronmicroscopy in that the uptake of cholesterol and lecithin coincides with the increase in smooth areas on the fracture faces of the erythrocyte membrane.
Assuntos
Colestase/sangue , Eritrócitos/metabolismo , Lipoproteínas/sangue , Sítios de Ligação , Membrana Celular/metabolismo , Membrana Celular/ultraestrutura , Eritrócitos/ultraestrutura , Humanos , Lipídeos/sangue , Microscopia Eletrônica , Ligação ProteicaRESUMO
Freeze etching showed that the loss of each of the major outer membrane proteins b, c or d in mutants of Escherichia coki K12 does not influence the morphology of fracture faces of the outer membrane. Mutants that possess a heptose-deficient lipopolysaccharide and which in addition are deficient in one or more major outer membrane proteins exhibit a reduction in the number of intramembranous particles of the outer membrane. Moreover it was shown that lipid phase transitions induce a lateral lipid protein separation in the outer membrane, similar to that found in the cytoplasmic membrane.
Assuntos
Proteínas de Bactérias/metabolismo , Membrana Celular/ultraestrutura , Escherichia coli/ultraestrutura , Mutação , Membrana Celular/metabolismo , Escherichia coli/metabolismo , Técnica de Congelamento e Réplica , Microscopia Eletrônica , Especificidade da EspécieRESUMO
As a basis for physicochemical studies on the membranes of the strictly anaerobic bacteria Veillonella parvula, Anaerovibrio lipolytica, and Megasphaera elsdenii, the fatty acyl and alk-1-enyl moieties on the phosphoglycerides of these organism were characterized. Uncommon is the high proportion of a heptadecenoic acyl and alk-1-enyl moiety in these three lactate-fermenting bacteria. In contrast to V. parvula and A. lipolytica, M. elsdenii contains high amounts of branched-chain acyl and alk-1-enyl moieties. Freeze-etching electron microscopy showed that the lipids of the plasma membranes of V. parvula and A. lipolytica go from the liquid crystalline to the gel state upon lowering of the temperature, indicating that the membrane lipids are predominantly in the fluid state. No lipid-protein segregation could be detected in the plasma membrane of M. elsdenii. This can be explained by the abundance of branched-chain fatty acyl and alk-1-enyl residues in the membranes of this organism which may prevent lipid-protein segregation during the lipid-phase transition.
Assuntos
Lipídeos , Veillonella/ultraestrutura , Vibrionaceae/ultraestrutura , Anaerobiose , Membrana Celular/ultraestrutura , Técnica de Congelamento e Réplica , Lipídeos/análise , Fosfatidiletanolaminas/análise , Fosfatidilserinas/análise , Fosfolipídeos/análise , Plasmalogênios/análise , Veillonella/análise , Veillonellaceae/análise , Veillonellaceae/ultraestrutura , Vibrionaceae/análiseAssuntos
Antibacterianos/farmacologia , Permeabilidade da Membrana Celular , Membrana Celular/metabolismo , Metabolismo dos Lipídeos , Membranas Artificiais , Proteínas/metabolismo , Acholeplasma laidlawii , Anfotericina B/farmacologia , Cátions Bivalentes/metabolismo , Cátions Monovalentes , Membrana Celular/efeitos dos fármacos , Membrana Celular/ultraestrutura , Permeabilidade da Membrana Celular/efeitos dos fármacos , Fenômenos Químicos , Físico-Química , Filipina/farmacologia , Técnica de Congelamento e Réplica , Técnica de Fratura por Congelamento , Modelos Biológicos , Relação Estrutura-AtividadeRESUMO
Calorimetric experiments showed a marked effect of Ca2+ and Mg2+ on the thermotropic behaviour of dimyristoyl phosphatidylglycerol. 2. Concentrations of Ca2+ and Mg2+ lower than 1 ion to 2 molecules of phosphatidylglycerol produced a shift of the phase transition to higher temperatures and an increase in the enthalpy change which is consistent with a closer packing of the lipid molecules in the liposomes. 3. Above the 1:2 ratio, freeze-fracture electron microscopy demonstrated typical "crystal" structures both in the presence of Ca2+ and Mg2+. In the presence of Mg2+ a metastable behaviour was noticed in the calorimetric experiments. 4. A Ca2+- and Mg2+-induced shift in the transition temperature and an increase in the enthalpy change was also observed in a 1:1 mixture of dimyristoyl phosphatidylglycerol and dimyristoyl phosphatidylcholine. However, these mixed samples remained liposomal in structure at any concentration of the divalent ions. 5. Liposomes prepared from a 1:1 mixture of dimyristoyl phosphatidylglycerol and dimyristoyl phosphatidylcholine in the absence of divalent cations are permeable in the range 10-50 degrees C. Bilayers of mixtures neutralized by Ca2+ or Mg2+ were demonstrated to be completely impermeable to K+, except in the vicinity of the phase transition. 6. The leak of ions from liposomes of a 1:1 mixture of dimyristoyl phosphatidylglycerol and dimyristoyl phosphatidylcholine in the vicinity of the phase transition temperature was considerably less in the presence of Ca2+ than in the presence of Mg2+. 7. It is concluded that there is a correlation between the calorimetric data and the permeability properties of dimyristoyl phosphatidylglycerol-containing bilayers with respect to the influence of Ca2+ and Mg2+.
Assuntos
Cálcio , Magnésio , Ácidos Mirísticos , Fosfatidilcolinas , Fosfatidilgliceróis , Fosfolipídeos , Lipossomos , Permeabilidade , Potássio , Temperatura , TermodinâmicaRESUMO
Protoporphyrin causes a photodynamic damage of the red blood cell membrane. After illumination of red blood cells in the presence of protoporphyrin three effects can be observed: 1. Red blood cell membranes show particle aggregation on the outer and inner fracture face, as seen in freeze-etch electron microscopy. 2. Electrophorograms of membrane proteins show an increasing protein association, not disrupted by sodium dodecyl sulfate. 3. The immunological response of A+ red cells to anti A serum is progressively retarded. It seems likely that these effects are interrelated consquences of the protoporphyrin-induced photodynamic membrane damage.
Assuntos
Eritrócitos/efeitos dos fármacos , Porfirias/sangue , Porfirinas/farmacologia , Protoporfirinas/farmacologia , Agregação Celular , Membrana Celular/efeitos dos fármacos , Membrana Celular/ultraestrutura , Escuridão , Eletroforese em Gel de Poliacrilamida , Eritrócitos/imunologia , Eritrócitos/ultraestrutura , Técnica de Congelamento e Réplica , Humanos , Luz , Microscopia Eletrônica , Fatores de TempoRESUMO
In the presence of Mg2+ ions phosphatidylglycerol shows supercooling which leads to the formation of a metastable gel phase. This contrasts with the behaviour of this negatively charged phospholipid in the presence of Ca2+ ions (Biochim. Biophys. Acta 39. (1974)432)9 It is demonstrated that the heat content of this phospholipid is dependent on the ionic environment.