A model for gramicidin A′-phospholipid interactions in bilayers

A model is proposed for the effect of gramicidin A on the order and structure of phospholipid dispersions. According to this model, the addition of gramicidin A influences the surrounding lipids via two independent mechanisms. The first arises from a drop in surface pressure for those lipids substantially bounded by gramicidin A. The second mechanism arises from the increase in the phospholipid headgroup spacing due to the small polar region of the polypeptide. The model provides an explanation for the currently available NMR, X-ray diffraction and Langmuir monolayer results. The model also suggests mechanisms for the ability of gramicidin A to trigger a transition of the lipid from the lamellar to hexagonal II phase, the dependence of this transition on the lipid chain length and the formation of a lamellar phase with lysophosphatidylcholine.Abbreviations NMR nuclear magnetic resonance - DMPC dimyristoylphosphatidylcholine - S molecular order parameter - CSA chemical shift anisotropy - DPPC dipalmitoylphosphati-dylcholine - LPC lysophosphatidylcholine     

A laser-T-jump study of the adsorption of dipolar molecules to planar lipid membranes

The adsorption of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) as well as of other dipolar molecules to the interface of artificial lipid membranes gives rise to a change of the dipole potential between the membrane interior and water. As a consequence of the adsorption of the neutral species, the conductance of planar membranes, observed in the presence of the macrocyclic ion carriers nonactin or valinomycin, may change by many orders of magnitude. Using this effect in combination with a laser-T-jump technique, the kinetics of the adsorption process were measured and were interpreted on the basis of a Langmuir-isotherm. A partition coefficient (at small concentrations) of _HA =4.7·10^–4 cm, a rate constant of desorption k _HA100 s^-1 and a maximum surface density N _D=7.7·10¹³/cm² were found. The concentration at half saturation is K _HA=2.7·10^-4 M.Using these values the membrane conductance induced by the ion carrier nonactin and the shape of the current-voltage relationship as a function of the ligand concentration in water was analyzed. A maxiumum dipole potential of V _D ^max =-239 m V and a contribution of b=3.1·10^-15V cm² per single adsorbed 2,4-D molecule was found. 74% of the dipole potential acts on the inner membrane barrier separating the two interfacial adsorption planes of nonactin. The remainder (26%) favours interfacial complex formation between nonactin and K⁺ from the aqueous phase. The data hold for membranes formed from dioleoyllecithin in n-decane.     

从二溴百里香醌的抑制效应分析融合膜电子传递的途径

甲基紫精(MV)系统中,在对类囊体膜的光合磷酸化(PSP)活力近于完全抑制的二溴百里香醌(DBMIB)浓度下,由类囊体残缺膜与线粒体嵴膜组成的融合膜PSP活力不仅不被抑制,反而受到不同程度的促进。在铁氰化钾(FeCy)系统中,DBMIB对类囊体膜的PSP活力不能完全抑制,同样浓度的DBMIB对融合膜的PSP活力有抑制效应。检测了不同膜在不同系统中,光下耗氧、放氧、FeCy还原和融合效应的关系等,论证了融合膜中电子传递的途径。     

Identification of G-proteins in rat parotid gland plasma membranes and granule membranes: presence of distinct components in granule membranes

We have identified by immunoblotting and ADP-ribosylation by cholera toxin and pertussis toxin the presence of Mr 43 and 46 KDa G_s, and 39 and 41 KDa G_i;.. subunits in rat parotid gland plasma membranes but not in granule membranes. A Mr 28 KDa polypeptide that served as substrate for ADP-ribosylation by both cholera toxin and pertussis toxin was present exclusively in granule membranes. Photoaffinity crosslinking of [-³²P]GTP showed the presence of high molecular weight GTP-binding proteins (Mr 160,100 KDa) in granule membranes. Six low molecular weight GTP-binding proteins (Mr 21–28 KDa) were differentially distributed in both plasma membranes and granule membranes. The present study identifies various GTP-binding proteins in rat parotid gland plasma membranes and granule membranes, and demonstrates the presence of distinct molecular weight GTP-binding proteins in granule membranes. These granule-associated GTP-binding proteins may be involved in secretory processes.     

Purification and properties of a F420-nonreactive,membrane-bound hydrogenase from Methanosarcina strain Gö1

The distribution of the F₄₂₀-reactive and F₄₂₀-nonreactive hydrogenases from the methylotrophic Methanosarcina strain Gö1 indicated a membrane association of the F₄₂₀-nonreactive enzyme. The membrane-bound F₄₂₀-nonreactive hydrogenase was purified 42-fold to electrophoretic homogeneity with a yield of 26.7%. The enzyme had a specific activity of 359 mol H₂ oxidized · min^-1 · mg protein^-1. The purification procedure involved dispersion of the membrane fraction with the detergent Chaps followed by anion exchange, hydrophobic and hydroxylapatite chromatography. The aerobically prepared enzyme had to be reactivated anaerobically. Maximal activity was observed at 80°C. The molecular mass as determined by native gel electrophoresis and gel filtration was 77000 and 79000, respectively. SDS gel electrophoresis revealed two polypeptides with molecular masses of 60000 and 40000 indicating a 1:1 stoichiometry. The purified enzyme contained 13.3 mol S^2-, 15.1 mol Fe and 0.8 mol Ni/mol enzyme. Flavins were not detected. The amino acid sequence of the N-termini of the subunits showed a higher degree of homology to cubacterial uptake-hydrogenases than to F₄₂₀-dependent hydrogenases from other methanogenic bacteria. The physiological function of the F₄₂₀-nonreactive hydrogenase from Methanosarcina strain Gö1 is discussed.Abbreviations transmembrane electrochemical gradient of H^- - CoM-SH 2-mercaptoethanesulfonate - F₄₂₀ (N-l-lactyl--l-glutamyl)-l-glutamic acid phospodiester of 7,8-didemethyl-8-hydroxy-5-deazariboflavin-5-phosphate - F₄₂₀H₂ reduced F₄₂₀ - HTP-SH 7-mercaptoheptanoylthreonine phosphate - Mb. Methanobacterium - PMSF phenylmethyl-sulfonylfluoride - Cl₃AcOH trichloroacetic acid     

Morphogenesis of the foetal membranes and placenta of the root-rat (Tachyoryctes splendens (Rüppel))

The morphogenesis of the foetal membranes and placenta of the root-rat Tachyoryctes splendens was studied by light microscopy. Implantation of the blastocyst is antimesometrial. The mode of implantation is secondary interstitial and the decidual reaction is similar to that in other rodents. Amniogenesis is by cavitation with a temporary open epamniotic cavity. Inversion of the yolk sac is complete but the disappearance of the parietal segment occurs relatively late. With the breakdown of both the decidua capsularis and parietalis, the yolk sac wall near the margins of the placenta becomes bathed in a pool of maternal blood and tissue debris resembling the haemophagous organ. The yolk sac villi are well vascularized. The allantoic cavity is persistent up to the limb bud stage. The definitive placenta is haemochorial and shows conspicuous endodermal sinuses or placental pits.     

High-affinity folate binding in human liver membranes

High-affinity binding of³H-folate in Triton X-100 solubilized membranes of human liver displayed characteristics, e.g. apparent positive cooperativity, which are typical of specific folate binding. Ultrogel^® AcA 44 chromatography of solubilized membranes saturated with³H-folate revealed a major peak of 100 kDa and a minor peak of 25 kDa. The 100 kDa peak could represent a hydrophobic membrane associated molecular form of the protein. This notion was supported by the fact that the two peaks had identical molecular weights as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis with immunoblotting.     

Platinum-supported Bilayer Lipid Membranes modified by ferrocene and its derivatives

The biferrocene-containing Schiff base complexes (1) and (2) were synthesized and characterized by elemental analyses and spectral data. The Pt-supported Bilayer Lipid Membranes (BLMs) modified by ferrocene and its derivatives were studied by cyclic voltametry (CV) and the electrochemical properties of this system are reported. The oxidation mechanism of electrocatalysis of ascorbic acid on the Pt-supported BLMs is discussed.