Effect of a diazafluoranthen derivative on phospholipases A study at the air-water interface

AC-3579 (2-N-methylpiperazinomethyl-1,3-diazafluoranthen 1-oxide) produces in rat hepatocytes a hypertrophy of the endoplasmic reticulum.Two possibilities that can explain this phenomenon are (1) that AC-3579 inactivates the phospholipases, and (2) that an AC-3579-lipid interaction hinders the enzymic activity.To demonstrate these hypotheses, a physicochemical model of biological membrane, the lipid-water interface, has been used. Dipalmitoyl dl-α-phosphatidylcholine was spread at the air-water interface, the enzymes (phospholipase A or phospholipase C) dissolved in the aqueous phase.The enzymic reaction was first studied with and without AC-3579 dissolved in the aqueous phase; no enzymic inactivation was observed. However in AC-3579- lipid complex completely inhibited the enzymic reaction in the case of phospholipase A.An explanation is given in terms of steric hindrance to the enzyme-substrate complex formation.     

Effect of phospholipid on trichosanthin adsorption at the air-water interface

Understanding the control of mitochondrial energy metabolism is central to knowing how mitochondria function within cells. Metabolic control analysis is the best approach available for studying the control of mitochondrial energy metabolism. Here I outline how metabolic control analysis has been used to help understand mitochondrial regulation, damage and pharmacology.     

Linear gramicidins at the air-water interface.

The behavior of four linear gramicidins, which differ by the nature of their 9, 11, 13, and 15 aromatic residues, together with a covalent "head to tail" retro GA-DAla-GA dimer, has been examined at the air-water interface. It is shown that all four "monomers" have almost the same molecular area, which is compatible with either a single-stranded or a double-stranded helical model, whereas it is suggested that retro GA-DAla-GA could adopt another conformation. The surface potential measurements agree with those of different groups of molecules characterized by their single-channel behaviors.     

Effect of surfactant type on surfactant--protein interactions at the air-water interface

The displacement of the proteins (beta-lactoglobulin and beta-casein) from an air-water interface by the nonionic (Tween 20 and Tween 60) and ionic (sodium dodecyl sulfate, cetyltrimethylammonium bromide, and lyso-phosphatidylcholine-lauroyl) surfactants has been visualized by atomic force microscopy (AFM). The surface structure has been sampled by the use of Langmuir-Blodgett deposition onto mica substrates to allow imaging in the AFM. In all cases, the displacement process was found to occur through the recently proposed orogenic mechanism (Mackie et al. J. Colloid Interface Sci. 1999, 210, 157-166). In the case of the nonionic surfactants, the displacement involved nucleation and growth of surfactant domains leading to failure of the protein network and subsequent loss of protein into the bulk phase. The surface pressure dependence of the growth of surfactant domains and the failure of the network were found to be the same for both Tween 20 and Tween 60, demonstrating that the breakdown of the protein film was dominated by the mechanical properties of the network. The displacement of protein by ionic surfactants was found to be characterized by nucleation of surfactant domains with little domain growth prior to failure of the network. The size of the domains formed by ionic surfactants was found to be limited by the strong intersurfactant repulsive forces between the charged headgroups. Screening of these charges led to an increase in the size of the domains. The surface pressure at which the network continuity was lost was found to be dependent on the type of surfactant and, in all cases, to occur at higher surface pressures than that required for nonionic surfactants. This has been attributed to surfactant-protein binding that initially strengthens the protein network at low surfactant concentrations. Evidence obtained from surface shear rheology supports this assertion.     

Amyloid-beta-sheet formation at the air-water interface

An amyloid(1-40) solution rich in coil, turn, and alpha-helix, but poor in beta-sheet, develops monolayers with a high beta-sheet content when spread at the air-water interface. These monolayers are resistant to repeated compression-dilatation cycles and interaction with trifluoroethanol. The secondary structure motifs were detected by circular dichroism (CD) in solution and with infrared reflection-absorption spectroscopy (IRRAS) at the interface. Hydrophobic influences are discussed for the structure conversion in an effort to understand the completely unknown reason for the natural change of the normal prion protein cellular (PrP(C)) into the abnormal prion protein scrapie (PrP(Sc)).     

Structural study of the DNA dipalmitoylphosphatidylcholine complex at the air-water interface

We present here results that demonstrate the formation of a complex of DNA with zwitterionic dipalmitoylphosphatidylcholine (DPPC) monolayer at the air-water interface in the presence of Ca2+ ions; in particular, we show that the presence of Ca2+ cations is essential for the formation of the complex of DPPC with DNA. We characterize the resulting structure by X-ray reflectivity and by null-ellipsometry. We show that DNA maintains its native double helix form when attached to the zwitterionic lipid monolayer, at difference with the case of ammine containing monolayers. Our findings are discussed in view of other works that recently appeared on the interaction of DNA with zwitterionic phospholipids, emphasizing the role of DPPC as a potential vector for transfer of genetic material into mammalian cells by nonviral gene therapy and also suggesting Langmuir/Blodgett layers of zwitterionic phospoholipids as a method for nonconventional DNA immobilization.     

Phase behaviour of stearic acid-stearonitrile mixtures. A thermodynamic study in bulk and at the air-water interface

The solid-liquid phase behaviour of stearic acid (SA) and stearonitrile (SN) in binary mixtures was investigated by differential scanning calorimetry (DSC), and the formation of SA-SN mixed monolayers at the air-water interface was followed by surface pressure-area (pi-A) measurements and by Brewster angle microscope (BAM) observation. The solid-liquid phase diagram is a eutectic type phase diagram, with the eutectic composition 0.90相似文献   

Molecular recognition of concanavalin A on mannoside diacetylene lipid monolayer at the air-water interface.

The interaction of p-10,12-pentacosadiyne-1-n-phenylamide alpha-D-mannopyranoside (MPDA) with protein concanavalin A (Con A) was studied at the air/water interface. The expansion of molecular area of PDA (10,12-pentacosadiynoic acid)/MPDA mixed monolayer after injection of Con A in subphase shows strong interaction between Con A and the monolayer. The maximum expansion of molecular area decreases as the molar ratio of MPDA increases due to the steric hindrance effect. By using enzyme mannosidase to cut-off the mannoside headgroup of MPDA, expansion of molecular area was greatly reduced, indicating that the binding of Con A is specific to the mannoside headgroup. The kinetics of the binding fits to the first order bimolecular reaction model. Fluorescence quenching of fluorescein isothiocyanate labeled Con A after injection into the subphase gives a direct proof of the molecular recognition.     

Structure of hydroxylated galactocerebrosides from myelin at the air-water interface.

Hydroxy-galactocerebrosides (mixed chain length, constituent of myelin membranes) from bovine brain are investigated as monolayers at the air-water interface with isotherms, fluorescence microscopy, x-ray reflectivity and grazing incidence diffraction. With grazing incidence diffraction a monoclinic tilted chain lattice is found in the condensed phase. According to x-ray reflectivity, the longest chains protrude above the chain lattice and roughen the lipid/air interface. On compressing the chain lattice, the correlation length increases by approximately 65%; obviously, the sugar headgroups are flexible enough to allow for lattice deformation. With fluorescence experiments, small coexisting fluid and ordered domains are observed, and there is lipid dissolution into the subphase as well. The dissolved hydroxy-galactocerebroside molecules reenter on monolayer expansion. The electron density profiles derived from x-ray reflectometry (coherent superposition) show that the chain-ordering transition causes the molecules to grow into the subphase.     

Enrichment of amyloidogenesis at an air-water interface

The aggregation of proteins or peptides into amyloid fibrils is a hallmark of protein misfolding diseases (e.g., Alzheimer's disease) and is under intense investigation. Many of the experiments performed are in vitro in nature and the samples under study are ordinarily exposed to diverse interfaces, e.g., the container wall and air. This naturally raises the question of how important interfacial effects are to amyloidogenesis. Indeed, it has already been recognized that many amyloid-forming peptides are surface-active. Moreover, it has recently been demonstrated that the presence of a hydrophobic interface can promote amyloid fibrillization, although the underlying mechanism is still unclear. Here, we combine theory, surface property measurements, and amyloid fibrillogenesis assays on islet amyloid polypeptide and amyloid-β peptide to demonstrate why, at experimentally relevant concentrations, the surface activity of the amyloid-forming peptides leads to enriched fibrillization at an air-water interface. Our findings indicate that the key that links these two seemingly different phenomena is the surface-active nature of the amyloid-forming species, which renders the surface concentration much higher than the corresponding critical fibrillar concentration. This subsequently leads to a substantial increase in fibrillization.     

ZL-DHP lignin model compound at the air-water interface

In this paper we present our surface chemistry studies of enzymatically polymerized, poly-coniferyl alcohol lignin model compound (dehydrogenate polymer a.k.a. ZL-DHP) at the air-water interface. Using the CHCl(3)/MeOH (5:1 v/v) spreading solvent, we found an average molecular area of ZL-DHP of approximately 1200 A(2). The monolayer expresses a high compressibility with a collapsed area of 500 A(2) and collapsed surface pressure of 28 mN m(-1). In the range of applied surface pressures, ZL-DHP polymer have no phase changes, as shown by the very high linearity (R=0.994) of absorbance vs. surface pressure cure. There was no symmetry transitions observed as shown by absence of shifts of absorption peak maximums.     

Two-dimensional diffusion of amphiphiles in phospholipid monolayers at the air-water interface.

Steady-state and time-resolved fluorescence spectroscopy has been used to examine lateral diffusion in dipalmitoyl-L-alpha-phosphatidylcholine (DPPC) and dimyristoyl-L-alpha-phosphatidylcholine (DMPC) monolayers at the air-water interface, by studying the fluorescence quenching of a pyrene-labeled phospholipid (pyrene-DPPE) by two amphiphilic quenchers. Steady-state fluorescence measurements revealed pyrene-DPPE to be homogeneously distributed in the DMPC lipid matrix for all measured surface pressures and only in the liquid-expanded (LE) phase of the DPPC monolayer. Time-resolved fluorescence decays for pyrene-DPPE in DMPC and DPPC (LE phase) in the absence of quencher were best described by a single-exponential function, also suggesting a homogeneous distribution of pyrene-DPPE within the monolayer films. Addition of quencher to the monolayer film produced nonexponential decay behavior, which is adequately described by the continuum theory of diffusion-controlled quenching in a two-dimensional environment. Steady-state fluorescence measurements yielded lateral diffusion coefficients significantly larger than those obtained from time-resolved data. The difference in these values was ascribed to the influence of static quenching in the case of the steady-state measurements. The lateral diffusion coefficients obtained in the DMPC monolayers were found to decrease with increasing surface pressure, reflecting a decrease in monolayer fluidity with compression.