Environmental topology and water availability modulates the catalytic activity of beta-Galactosidase entrapped in a nanosporous silicate matrix

In the present work we studied the catalytic activity of E. coli β-Gal confined in a nanoporous silicate matrix (Eβ-Gal) at different times after the beginning of the sol-gel polymerization process. Enzyme kinetic experiments with two substrates (ONPG and PNPG) that differed in the rate-limiting steps of the reaction mechanism for their β-Gal-catalyzed hydrolysis, measurements of transverse relaxation times (T2) of water protons through 1H-NMR, and scanning electron microscopy analysis of the gel nanostructure, were performed. In conjunction, results provided evidence that water availability is crucial for the modulation observed in the catalytic activity of β-Gal as long as water participate in the rate limiting step of the reaction (only with ONPG). In this case, a biphasic rate vs. substrate concentration was obtained exhibiting one phase with catalytic rate constant (kcA), similar to that observed in solution, and another phase with a higher and aging-dependent catalytic rate constant (kcB). More structured water populations (lower T2) correlates with higher catalytic rate constants (kcB). The T2-kcB negative correlation observed along the aging of gels within the 15-days period assayed reinforces the coupling between water structure and the hydrolysis catalysis inside gels.Fil: Burgos, Martha Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Velasco, Manuel Isaac. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Acosta, Rodolfo Héctor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Perillo, Maria Angelica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentin

Evidence of tryglyceride-phase incorporation into artificial bilayers for studying lipid droplets biogenesis

Lipid Droplets (LD) are intracelular structures consisting on an apolar lipid core - composed mainly of triglycerides (TG) and steryl esters- which is surrounded by a phospholipid and protein monolayer. LDs originate in the ER bilayer, where TG synthesis concludes. The mechanisms underlying TG nucleation, size maduration and budding-off from the ER membrane are a matter of current investigations and the role of dewetting from cytosolic-bilayer interface appears to play a critical role. In order to contrast the nano-sized "blisters" of TG that some authors predict1, here we formed free-standing bilayers by transferring films of a monolayer of mixed phosphatidylcholine(EPC)/TG in coexistence with TG microlenses (i.e. an excluded TG phase floating in the surface). These membranes were characterized by adding them the solvatochromic fluorescent probe Nile Red (NR) and observing them under spectral confocal microscope. Such bilayers exhibit fluorescence emission spectra comparable of bilayers of vesicles with similar composition (POPC and TO). By comparison with literature data and fluorescence spectra of EPC and TG monolayers, the peaks could be assigned to different phases, namely 1) PC membranes (λemmax=630 nm ) bilayer and bilayer) and 2) TG isotropic phase (λemmax=570 nm ). No microscopic structures could be observed at λ emmax=570 nm. Diffusion of NR under this TG phase was characterized using FRAP analysis yielding values (D=2 μm2s ) typical of model bilayer membranes, suggesting that the probe is diffusing in a 2D structure. This system appears appropiate for describing which is the distribution of the TG phase, that is, homogeneously among the intrabilayer space or in nanoscopic "blisters", by evaluating diffusion times obtained by FCS and FRAP.Fil: Caruso, Benjamin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Mangiarotti, Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; ArgentinaFil: Wilke, Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; ArgentinaFil: Perillo, Maria Angelica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaXLVII Reunión Anual de la Sociedad Argentina de BiofísicaLa PlataArgentinaSociedad Argentina de BiofísicaUniversidad Nacional de La plata. Facultad de Ciencias Médica

Phospholipid multilamellar vesicles entrapping phenothiazine photosensitizers. Preparation, characterization and evaluation of their photodynamic properties

The aim of the present paper was to optimize the properties of phenothiazine photosensitizers (PSs), Azure B and its monobrominated derivative. They were entrapped in multilamellar liposomes of egg phosphatidylcholine (EPC) and dipalmitoylphosphatidylcholine (dpPC). The higher partition coefficient of both PSs in the EPC/water system compared with that of both PSs in the dpPC/water system allowed the selection of EPC to be used for the development of third generation photosensitizers. The optimal phospholipid/phenothiazine ratio and the location of these dyes in the lipid bilayer systems were established. These dyes were found to be located within the polar head group region of the lipid bilayer, which would enhance the effectiveness of the irradiation procedure. In addition, the encapsulation of both photosensitizers in liposomes led to a decrease in the aggregation of these compounds, and consequently to an increase in their singlet oxygen quantum yield (ϕΔ). The encapsulation of the PSs in lipid vesicles significantly increased their photochemical reactivity, doubling the ϕΔ value of AzBBr and increasing that of AzB by 60%. The results obtained demonstrate that the vehiculization of these PSs in liposomes allowed the development of third generation photosensitizers with better photochemical properties to be used in potential therapeutic applications.Fil: Vara, Jimena. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Farmacia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Unidad de Investigación y Desarrollo en Tecnología Farmacéutica. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Unidad de Investigación y Desarrollo en Tecnología Farmacéutica; ArgentinaFil: Sanchez, Julieta Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Química. Cátedra de Química Biológica; ArgentinaFil: Perillo, Maria Angelica. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Química. Cátedra de Química Biológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Ortiz, Cristina Susana. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Farmacia; Argentin

Effects of Gabaergic phenols on phospholipid bilayers as evaluated by 1H-NMR

The phenols propofol and thymol, and lately carvacrol, eugenol and chlorothymol, have been shown to act as positive allosteric modulators on GABAA receptor, which is the main inhibitory receptor of the central nervous system. GABAA receptor is an intrinsic membrane protein which activity may be affected by surface-active compounds and by physical changes in the membrane. Recently, we demonstrated that these phenols interacted with the lipid membrane phase, suggesting their anesthetic activity could be the combined result of their specific (with receptor proteins) as well as nonspecific (with surrounding lipid molecules) interaction modulating the supramolecular organization of the receptor environment. In the current study, by using 1H-NMR spectroscopy, we have investigated the effects of the insertion and the possible preferential location of the five phenol derivatives with GABAergic activity on EPC membranes. The results indicate that all compounds are able to insert in EPC phospholipid vesicles and to locate in the region between the polar group (choline molecule), the glycerol and the first atoms of the acyl chains, being the more lipophilic compounds (propofol and chlorothymol) that seem to prefer a deeper bilayer insertion. The location of the phenol molecules would reduce the repulsive forces among phospholipids head groups allowing closer molecular packing and finally diminishing the mobility of the hydrocarbon chains, as revealed by 1H spin relaxation times.Fil: Reiner, Gabriela de Las Nieves. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentina. Universidade Estadual de Campinas; Brasil. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Fraceto, Leonardo Fernandes. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Paula, Eneida de. Universidade Estadual de Campinas; BrasilFil: Perillo, Maria Angelica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Garcia, Daniel Asmed. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentin

V-shape" molecular configuration of wax esters of jojoba oil in a Langmuir film model

The aim of the present work was to understand the interfacial properties of a complex mixture of wax esters (WEs) obtained from Jojoba oil (JO). Previously, on the basis of molecular area measurements, a hairpin structure was proposed as the hypothetical configuration of WEs, allowing their organization as compressible monolayers at the air-water interface. In the present work, we contributed with further experimental evidence by combining surface pressure (π), surface potential (ΔV), and PM-IRRAS measurements of JO monolayers and molecular dynamic simulations (MD) on a modified JO model. WEs were self-assembled in Langmuir films. Compression isotherms exhibited π lift-off at 100 Å 2 /molecule mean molecular area (A lift-off ) and a collapse point at π c ≈ 2.2 mN/m and A c ≈ 77 Å 2 /molecule. The ΔV profile reflected two dipolar reorganizations, with one of them at A > A lift-off due to the release of loosely bound water molecules and another one at A c < A < A lift-off possibly due to reorientations of a more tightly bound water population. This was consistent with the maximal SP value that was calculated according to a model that considered two populations of oriented water and was very close to the experimental value. The orientation of the ester group that was assumed in that calculation was coherent with the PM-IRRAS behavior of the carbonyl group with the C=O oriented toward the water and the C-O oriented parallel to the surface and was in accordance with their orientational angles (∼45 and ∼90°, respectively) determined by MD simulations. Taken together, the present results confirm a V shape rather than a hairpin configuration of WEs at the air-water interface.Fil: Caruso, Benjamin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Química. Cátedra de Química Biológica; ArgentinaFil: Martini, María Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Metabolismo del Fármaco. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Metabolismo del Fármaco; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; ArgentinaFil: Pickholz, Mónica Andrea. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Perillo, Maria Angelica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Química. Cátedra de Química Biológica; Argentin

Sensing molecular organizational changes through the catalytic activity of acetylcholinesterase from erythrocyte membranes in Langmuir-Blodgett films

Langmuir films prepared from bovine erythrocyte membranes (LFBEM) were studied and transferred to alkylated glasses (Langmuir-Blodgett films, LBBEM) in order to assess the effects of membrane molecular packing on Bovine Erythrocyte Acetylcholinesterase (BEA) catalytic activity. Surface pressure (π) vs Area isotherms showed three 2D-transitions at ~7, ~18 and ~44 mN/m and a collapse pressure at πc = .49 mN/m. The 0?12?0 mN/m compression-decompression cycles resulted reversible while those 0?40?0 mN/m exhibited a significant hysteresis. Taken together, EFM, BAM and AFM images and the stability of the film after 3C-D cycles, we can suggest that over the air-water interface as well as over the silanized glass substrate the surface is mostly covered by a monolayer with a few particles dispersed. Acetylthiocholine hydrolysis was assayed with BEA in bovine erythrocyte membrane suspensions (SBEM) and in LBBEM packed at 10 (LBBEM,10) and 35 mN/m (LBBEM,35), which gave the following kinetic parameters: Vmax = .3.41 ± 0.15, 0.021 ± 0.002 and 0.030 ± 0.003 nmol.min− 1·μg prot− 1 and KM = .0.11 ± 0.02, 0.047 ± 0.017 and 0.026 ± 0.017 mM, respectively. Although from SBEM to LBBEM we lost active enzyme, the catalytic efficiency (Vmax/KM) increased ~750 times. Eugenol and 1,8-cineol inhibited BEA catalytic activity in LBBEM,35. Our results demonstrate the transmission of information between the membrane and the environment within the subphase immediately below the membrane, where anchored proteins are hosted. This was reflected by the membrane packing-induced modulation of BEA catalytic activity. Furthermore, LBBEM provides a proof of concept for the development of biosensors to screen new green pesticides acting through BEA interaction.Fil: Felsztyna, Iván. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Turina, Anahi del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Perillo, Maria Angelica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Clop, Eduardo Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentin

Membrane topology modulates β-galactosidase activity against soluble substrates

The effect of bio-surfaces of contrasting curvature, on the kinetic parameters of ortho-nitrophenyl-β-D-galactopiranoside hydrolysis catalyzed by E. coli β-galactosidase, was investigated. The self-aggregating state and structure of the amphiphiles (Phosphatidylcholine, Lubrol-PX, Triton X-100, DocNa, SDS and CTAB) were inferred from their c.m.c. values and light-scattering measurements. Low curvature phosphatidylcholine or mixed phosphatidylcholine-detergent vesicles increased V max without affecting K M. High curvature micellar structures containing ionic detergents modulated negatively the enzyme activity (decreased or abolished V max and increased K M). Neither micelles containing non-ionic detergents nor the amphiphiles in a monomeric form, affected enzyme activity. CTAB at a concentration bellow its c.m.c but incorporated into a bilayer, became an activator (K M decreased respect to the control). Non-enzymatic interfacial hydrolysis of the substrate was discarded. Enzyme-membrane interaction and membrane elasticity, were evaluated using monomolecular layers at the air-water interface. Beyond particular molecular structures, topology affected the direction of the modulatory effects exerted by these amphiphiles on β-galactosidase activity. © 2002 Elsevier Science B.V. All rights reserved.Fil: Sanchez, Julieta Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Perillo, Maria Angelica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentin

α-Amylase kinetic parameters modulation by lecithin vesicles: Binding versus entrapment

The effect of α-amylase-lipid interaction and entrapment inside lipidic soybean lecithin (PC) vesicles on the kinetic parameters of the enzyme was investigated. Human saliva was used as enzyme source and starch as substrate. Reaction kinetics were followed by measuring the consumption of starch as revealed by the decrease in the absorbance at 600 nm of the I2-starch complex. The presence of PC induced a decrease in A600 at low concentrations; above 0.1 g PC/l light scattering became important and an increase in absorbance was observed as a function of lipid concentration. These effects were taking into account in the interpretation of results. Multilamellar vesicles (MLVs) and giant unilamellar vesicles (GUVs) were prepared by established procedures; enzyme was 'entrapped' by the inclusion of saliva, conveniently diluted, in the buffer used for lipid dispersion during the preparation of vesicles. The kinetic parameters K(M) and V(max) were determined by adjusting saturation curves to the Michaelis-Menten equation by a computer assisted nonlinear regression analysis by the least squares method. The presence of PC in MLVs induced an increment of the value of K(M) of α-amylase for starch as the substrate both in the condition we designated as 'entrapped' and when the enzyme was applied to the already formed liposomes ('untrapped'). The effects exerted by PCs MLVs on K(M) and V(max) were statistically significant only at the highest PC/protein mass ratio used (28 g/g). GUVs affected amylase K(M) only in some of the 'entrapped' samples at random suggesting certain aggresiveness of the GUVs preparation method. V(max) decreased significantly only in the 'entrapped' samples. The higher effect of MLVs in reducing the affinity of the enzyme for starch compared with that of GUVs is probably due to a higher protein adsorbing capacity of the lower molecular packing, higher surface tension and more curved MLV surface compared with the GUV surface. The binding of the enzyme to the lipidic surface is reversible and can be modulated by the presence of high salt concentrations or with the pH of the media which affect the surface electrostatics of both, the lipidic and the protein surfaces. The conclusions drown from the present experiments represent the average behavior of all the isozymes that represent α-amylase from human saliva and may be useful for understanding α-amylase activity in heterogenous media of physiological and technological importance. Copyright (C) 2000 Elsevier Science B.V.Fil: Sanchez, Julieta Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Química. Cátedra de Química Biológica; ArgentinaFil: Perillo, Maria Angelica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Química. Cátedra de Química Biológica; Argentin

Membrane adsorption or penetration differentially modulates β-galactosidase activity against soluble substrates

We investigated if in complex environments, like those where β-galactosidase activity is usually assayed, the kinetics of hydrolysis against soluble substrates could be modulated through enzyme-surface interactions. Kinetic parameters were determined using ortho-nitrophenyl-β-D-galactopiranoside (ONPG) as substrate, in the absence or presence of multilamellar vesicles (MLVs) of pure phosphatidyl cholines (PCs) or PCs:cholesterol mixtures, by visible spectroscopy. Light scattering was carefully corrected by three different methods obtaining similar results. The spectroscopic behavior of the reaction product in the presence of liposomes was also taken into account in order to avoid overestimating the reaction rate calculated from absorbance data. At low [PC] (<0.0024 mM) KM and Vmax decreased compared with the control in the absence of lipids. At high [PC] (1.2 mM), enzyme interaction with highly packed bilayers of dpPC induced an increment in both kinetic parameters. Both kinetic parameters decreased upon the interaction with low packed bilayers (soybean PC) at very low concentration (24 μM) but at higher concentration (1.2 mM) only an increment in Vmax was observed. The dpPC MLVs samples used were four times bigger than those of PCsoybean (approximately 1 μm mean diameter) as measured by quasi elastic light scattering. The increments in Vmax were due to a modulation of the kinetics of the enzymatic reaction and not to non-enzymatic hydrolysis of ONPG at the vesicle-water interface. Enzyme-membrane interaction was confirmed using monomolecular-layers at the air-water-interface. Interestingly, β-galactosidase showed a higher tendency to be localized at a lipid-water interface compared with the free air-water interface; membrane penetration was favored in lower packed membranes. Differences in surface curvature, and thus in surface molecular packing and hydration, might account for the effects observed as the main modulating factor. Our results suggest that β-galactosidase activity was differentially modulated according to the enzyme possibility to penetrate or just be adsorbed to a dimensionality restricted space. © 2002 Elsevier Science B.V. All rights reserved.Fil: Sanchez, Julieta Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Perillo, Maria Angelica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentin

Surface behavior of jojoba oil alone or in mixtures with soybean oil

In the present work, the behavior of jojoba oil (JO), soybean oil (SBO) and JO/SBO mixtures at the air–water interface was studied. Experiments were performed by applying the Langmuir balance method. Monomolecular layers were prepared on a water subphase, which were subjected to lateral compression in a rectangular trough, using a Wilhelmy plate as a surface pressure transducer. The results showed that JO form stable and reproducible monomolecular layers at the air–water interface. The surface pressure–area isotherms showed an extremely low collapse pressure (πc) of 2.3 mN/m, a mean molecular area of 210 Å2/molecule and a compressional modulus at πc of 23 mN/m, characteristic of liquid expanded monolayers. The compression–expansion cycle exhibited an unusual hysteresis, leading to π values higher in the expansion isotherm compared to those in the compression isotherm at the same mean molecular area. This behavior was interpreted as an increase in the hydration level of the polar groups during the lateral compression, which forced it to be immersed in the subphase. This excess hydration free energy, released to the environment during the compression process, was equivalent to ΔΔG = −94 J/molecule. SBO and JO formed non-ideal mixtures, stabilized by attractive interactions at all proportions. The values of surface tension calculated for the water/monolayer interface (γw/m = 60–70 mN/m for JO content between 0 and 100%) as well as the bending energy of this interface (700 kT units for micro-emulsion particles of 20 nm radii) were extremely high compared with those needed to obtain spontaneous emulsification (0.01 mN/m). This indicated that SBO/JO/water micro-emulsion require the addition of surfactants to become thermodynamically stable.Fil: Perillo, Maria Angelica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Química. Cátedra de Biofísica Química; ArgentinaFil: Maestri, Damian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Química. Cátedra de Química Organica; Argentin