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PubMed1991

Hormone-responsive survival of mammary gland explants from the pregnant tammar wallaby (Macropus eugenii) in the absence of exogenous hormones and growth factors.

1. The level of beta-lactoglobulin mRNA increased maximally in mammary explants from late pregnant tammars cultured for 3 days in media containing either prolactin or insulin, cortisol and prolactin. 2. The same level of accumulation occurred when explants were first cultured for 4 days in a chemically defined medium with no exogenous hormones, serum or growth factors, suggesting that the tissue remains viable and hormone-responsive during the initial incubation. 3. Mammary explants cultured for 4 days in medium with no hormones demonstrated a progressive increase in the rate of RNA and DNA synthesis suggesting that the tissue is under a positive autocrine/paracrine stimulus.

Animals↗
PubMed1979

On the determination of association constants of proteins by electrophoresis measurements.

During the electrophoresis of a reversibly associating substance the concentration profile is determined by diffusion, migration and reaction. The influence of the diffusion can be eliminated by extrapolating the concentration profiles, taken at different times and suitably transformed, to infinite time. This leads to a profile which reflects migration and reaction only (Gilbert profile). From this the association constant can be deduced. Preliminary experiments with beta-lactoglobulin A show the feasibility of the method.

Chemical Phenomena↗
PubMed1982

On the nanosecond mobility in proteins. Edge excitation fluorescence red shift of protein-bound 2-(p-toluidinylnaphthalene)-6-sulfonate.

The fluorescence of 2-(p-toluidinylnaphthalene)-6-sulfonate associated with beta-lactoglobulin, beta-casein, and bovine and human serum albumins are shown to depend on excitation wavelength. A long-wave shift of the spectra is observed at the long-wave edge excitation, reaching 10 nm and above. A similar phenomenon is found in glucose glass and in glycerol at +1 degrees C, i.e., in systems with delayed dipolar solvent relaxation, but not in liquid solutions. This phenomenon is proposed to be based on relaxation processes in the excited state. There exists a distribution of chromophore microstates with different interactions with surrounding groups which results in heterogeneous broadening of the electronic spectra and allows photoselection of a part of this distribution, being characterized by a low transition energy. The fast structural relaxation results in an altered distribution and, if this is the case, the effect of edge excitation of fluorescence spectra is not observed. If the structural relaxation during the excited state lifetime is absent, this effect is maximal. This interpretation is in agreement with results on the influence of red edge excitation on the low-temperature fluorescence spectra of dyes and with the data on time-resolved nanosecond fluorescence spectroscopy. The results of this work strongly support the significant dye fluorescence spectral shifts on protein binding, being determined not only by polarity changes in their environment, but also by relaxation properties of protein groups in this environment. These results also indicate that on the nanosecond time scale, the structural relaxation around the excited chromophore in proteins may be incomplete.

Animals↗
PubMed1990

Prolactin stimulates milk protein promoter in CHO cells cotransfected with prolactin receptor cDNA.

A functional biological system was developed by cotransfecting mammalian cell lines with the cDNA of the prolactin receptor (PRL-R) and a fusion gene containing the promoter of the milk protein, ovine beta-lactoglobulin linked to the coding sequence of the chloramphenicol acetyltransferase (CAT) gene. Surprisingly, this system is effective even if a non-mammary cell line is used, since Chinese hamster ovary (CHO) cells transfected both transiently and stably with PRL-R cDNA respond to PRL, as observed by stimulation of the reporter gene. This newly developed system should help precisely define the functional domains of both the PRL-R molecule and of the regulatory elements of a PRL target gene.

Animals↗
PubMed1996

Characteristics of phosphatidic acid-containing lipoproteins which selectively inhibit bitter taste: high affinity to frog tongue surface and hydrophobic model membranes.

In previous studies (Katsuragi and Kurihara (1993) Nature 365,213--214; Katsuragi et al. (1995) Pharm. Res. 12,658--662) we showed that a lipoprotein composed of phosphatidic acid (PA) and beta-lactoglobulin (LG) selectively suppressed the taste responses to bitter substances without affecting those to other taste stimuli in the frog and man, while complexes composed of other lipids except for phosphatidylserine and LG had little inhibitory activity. In the present study, we found that the lipoproteins having inhibitory activity are adsorbed on the frog tongue surface, while those having no inhibitory activity are not adsorbed. We also examined adsorption of the lipoproteins on model lipid membranes coated on a quartz-crystal microbalance by measuring changes in its frequency. The lipoproteins having inhibitory activity were well adsorbed on the hydrophobic lipid membranes, while the lipoproteins having no inhibitory activity were little adsorbed on the membranes. It seems that receptor sites for bitter substances on the taste cell membranes are hydrophobic and those for other taste stimuli such as salts, acids and sugars are hydrophilic. Hence, the binding of PA-LG to hydrophobic sites of the receptor membranes will lead to selective inhibition of bitterness.

Adsorption↗
PubMed1996

Protein partitioning in weakly charged polymer-surfactant aqueous two-phase systems.

The study includes partitioning of proteins in aqueous two-phase systems consisting of the polymer dextran and the non-ionic surfactant C12E5 (pentaethylene glycol mono-n-dodecyl ether). In this system a micelle-enriched phase is in equilibrium with a polymer-enriched phase. Charges can be introduced into the micelles by the addition of charged surfactants. The charge of the mixed micelles is easily varied in sign and magnitude independently of pH, by the addition of different amounts of negatively charged surfactant, sodium dodecyl sulphate (SDS), or positively charged surfactant dodecyl trimethyl ammonium chloride (DoTAC). A series of water-soluble model proteins (BSA, beta-lactoglobulin, myoglobin, cytochrome c and lysozyme), with different net charges at pH 7.1, have been partitioned in non-charged systems and in systems with charged mixed micelles or charged polymer (dextran sulphate). It is shown that partition coefficients for charged proteins in dextran-C12E5 systems can be strongly affected by addition of charged surfactants (SDS, DoTAC) or polymer (dextran sulphate) and that the effects are directly correlated to protein net charge.

Buffers↗
PubMed2005

Characterization of polyanion-protein complexes by frontal analysis continuous capillary electrophoresis and small angle neutron scattering: effect of polyanion flexibility.

The binding constant (K(obs)) for the beta-lactoglobulin-poly(vinylsulfate) (BLG-PVS) complex was measured by frontal analysis continuous capillary electrophoresis at pH values above the isoelectric point of BLG, and the persistence length (L(p)) of PVS was measured by small angle neutron scattering, to examine the effect of polyelectrolyte chain stiffness on its binding efficiency to proteins. The values of K(obs) and L(p) were compared with those of BLG-PSS and BLG-PAMPS (poly(2-acrylamido-2-methylpropanesulfonate)) reported previously. The relationship between K(obs) and L(p) was reciprocal, indicating that protein binding is enhanced by the flexibility of the polyanion, at least in the case where the net protein charge is negative. In addition, at a fixed pH, the polymer systems displayed a similar ionic strength dependence of K(obs). This similarity was consistent with the proposal that the binding properties of PVS and PAMPS polyanions are governed purely by electrostatic interactions and are independent of their molecular structure.

Electrophoresis, Capillary↗
PubMed2005

Characterisation of proteins in the milk of fur seals.

Milk protein composition was investigated throughout the lactation periods of the Australian fur seal (Arctocephalus pusillus doriferus) and Antarctic fur seal (Arctocephalus gazella). The mean protein content of the milk was found to be 10.9% and 10.6% respectively. The concentration of total protein did not change during lactation, although a decline in casein content of the milk in late lactation was apparent. Milk protein concentration during a foraging/suckling cycle of the Antarctic fur seal analysed at the time of arrival on shore, and 24 h and 72 h after arrival was 12.8%, 11.4% and 12.5% respectively. Re-feeding animals at 72 h resulted in a significant increase in milk protein content to 14.9%. Characterisation of milk protein by SDS-PAGE analysis revealed 5 casein and 10 major whey protein bands. Amino-terminal sequencing indicated that the majority of the whey fraction of the milk is beta-lactoglobulin (beta-LG). The limited amino acid sequence indicated 3 different beta-LGs were secreted in the milk. Subsequently, RT-PCR was used to extend the sequence of one of the beta-LGs and translation of the 464 bp fragment indicated that it shared 79% sequence identity with feline beta-LG II.

Amino Acid Sequence↗
PubMed2005

Gene transfection and expression in a primary culture of mammary epithelial cells isolated from lactating sows.

Porcine mammary epithelial cells (PMECs) were isolated from lactating sow mammary glands and cultured on a matrix gel. Primary culture cells expressed significant amounts of the specific marker cytokeratin as determined by immunohistochemistry, and exhibited mammary-specific functions, such as transcription of alpha-lactalbumin, beta-casein and beta-lactoglobulin genes. They also formed mammospheres when the medium was supplemented with lactogenic hormones. The PMECs were used to study gene transfer and expression in vitro. A gene encoding enhanced green fluorescent protein (EGFP) was used as a reporter and two constructs were investigated, pEGFP-N1 (a vector constructed with a CMV promoter followed by the EGFP gene) and pGB562/GFP (a mammary gland-specific expression vector with regulatory sequences from the goat beta-casein gene linked to EGFP). The efficiency of DNA transfer into the cultured PMECs was about 20-30%. GFP expression in the pGB562/GFP-transfected PMECs was markedly stimulated by prolactin supplements in the medium. The established PMECs maintained optimal gene expression from 1 to 20 passages and appeared to provide an efficient and convenient system for assessing the expression of transgenes containing mammary gland-specific promoters.

Animals↗
PubMed2006

Surface dilational rheology of mixed adsorption layers at liquid interfaces.

The dilational rheology for mixed solutions of surface active compounds is easy to measure with existing methods, however, there are very few attempts only to analyse the resulting data on the basis of a theoretical model. Models by Jiang et al., Joos, and by Lucassen and van den Tempel (for single compounds) are compared here and applied to experimental data. The mentioned models converge to each other after some small modifications and represent a very good scientific background for studies of the mechanical behaviour of mixed adsorption layers. As example, the experimental results for mixed solutions containing a globular protein (beta-lactoglobulin) and a non-ionic surfactant (alkyl dimethyl phosphine oxide) are analysed by the obtained dependencies, using some new proposed numerical procedures.

Adsorption↗
PubMed2004

Electrostatic effects on the yield stress of whey protein isolate foams.

The mechanisms responsible for foam structure are of practical interest within the food industry. The yield stress (tau) of whey protein isolate (WPI) foams as affected by electrostatic forces was investigated by whipping 10% (w/v) protein solutions prepared over a range of pH levels and salt concentrations. Measurements of foam overrun and model WPI interfaces, i.e. adsorption kinetics as determined via dynamic surface tension and dilatational rheological characterization, aided data interpretation. Interfacial measurements were also made with the primary whey proteins, beta-lactoglobulin (beta-lg) and alpha-lactalbumin (alpha-la). Yield stress of WPI foams was dependent on pH, salt type and salt concentration. In the absence of salt, tau was highest at pH 5.0 and lowest at pH 3.0. The addition of NaCl and CaCl2 up to 400 mM significantly increased tau at pH 7.0 but not at pH 3.0. Furthermore, at pH 7.0, equivalent molar concentrations of CaCl2 as compared to NaCl increased tau to greater extents. Salts had minimal effects on tau at pH 5.0. Comparisons with interfacial rheological data suggested the protein's capacity to contribute towards tau was related to the protein's potential at forming strong, elastic interfaces throughout the structure. The dynamic surface tension data for beta-lg and alpha-la were similar to WPI, while the interfacial rheological data displayed several noticeable differences.

Adsorption↗
PubMed2004

Effect of pH and ionic strength on competitive protein adsorption to air/water interfaces in aqueous foams made with mixed milk proteins.

Quantitative analysis of competitive milk protein adsorption to air/water interfaces in aqueous foam was performed by capillary electrophoresis (CE). Foams were made by whipping protein solutions, in which skim milk powder (SMP) and whey protein isolate (WPI) were mixed at 0.5% protein in different proportions at different pH values and NaCl concentrations. Preferential adsorption of beta-casein into foam phases occurred under most solution conditions, if partial dissociation of the casein micelles had occurred. Preferential adsorption of beta-casein was not observed with added Ca2+, due to the re-association of casein micelles. Enrichment of caseins into the foam phase was more apparent than that of whey proteins. The foamability of SMP demonstrated a continuous improvement due to the gradually increasing dissociation of casein micelles when the concentration of NaCl increased from 0 to 0.8 M. The foamability of WPI increased when NaCl concentration rose from 0 to 0.1 M, and decreased with further increase in NaCl concentration. NaCl at low concentration (I < or = 0.4) did not show a significant effect on the competitive adsorption among milk proteins, indicating that electrostatic interactions do not play a key role in competitive adsorption. NaCl at higher concentration, e.g., 0.6 M, caused less whey protein to be adsorbed to the air/water interfaces. The whippability of WPI was highest at pH 4.5 and lowest at pH 3, and that of SMP was the opposite. The proportions of beta-lactoglobulin and alpha-lactalbumin in the foam phase were lower at acidic pH and higher at basic pH, compared with that at natural pH of WPI.

Adsorption↗
PubMed2006

ESR and NMR spectroscopy studies on protein oxidation and formation of dityrosine in emulsions containing oxidised methyl linoleate.

Oxidised lipids are reported to interact with proteins causing undesirable changes in nutritional and functional properties including a loss of amino acids, cross-linking and damage to proteins and DNA. ESR spectroscopy with spin trapping was used to study the type of radical species generated in methyl linoleate and the transfer of the radical to protein beta-lactoglobulin. Antioxidants vitamins C and E reduced lipid oxidation and subsequent transfer of the radical to the protein as shown by the shape and size of the radical adduct. Changes to protein molecular structure due to oxidation were investigated by multidimensional NMR spectroscopy and liquid chromatography. NMR spectra indicated that as a result of oxidation and protein denaturation, there was an increase in structural flexibility and some initially protected backbone amide groups were exposed as they become sharper and easily identifiable. Dityrosine was detected in all samples tested which is indicative of oxidative damage to proteins. Monitoring tyrosyl radicals and formation of dityrosine is of practical value in order to enhance the acceptability, nutritional and safety aspects of proteins.

Electron Spin Resonance Spectroscopy↗
PubMed2004

Antigen-specific secretory IgA antibodies in the gut are decreased in a mouse model of food allergy.

BACKGROUND: A large body of evidence implicates IgA antibodies in the immune response to pathogens present in the gut. Whether IgA antibodies play a similar role in food allergy remains to be determined. OBJECTIVE: We sought to characterize beta-lactoglobulin (BLG)-specific serum and secretory IgA antibody production in the gut and to define the role of antigen-induced cytokines in IgA production in a murine model of food allergy. METHODS: BLG-specific IgA antibodies were measured in the sera and feces of mice anaphylactic or tolerant to BLG. The number of antibody-secreting cells in the spleen and Peyer's patches was determined by means of ELISPOT. Mesenteric lymph node cells and Peyer's patch T cells were transferred to naive mice, and antibody production in the sera and feces in recipient mice, as well as antibody-secreting cell numbers, were measured. RESULTS: Serum IgA antibody titers were strongly increased in anaphylactic mice. In contrast, BLG-specific IgA antibody titers were increased in feces but not in sera from tolerant mice. These results were correlated with an increased number of BLG-specific IgA-secreting cells in Peyer's patches from tolerant mice. The adoptive transfer of Peyer's patch CD3+ cells from tolerant mice induced an increased number of IgA-secreting cells preferentially in the Peyer's patches of naive recipient mice. Furthermore, an increase of BLG-induced IL-10 and TGF-beta levels was found at IgA production sites. CONCLUSIONS: These results suggest a role for secretory IgA in tolerance mechanisms to foods. Peyer's patch CD3+ cells are primarily involved by favoring IgA production through the release of IL-10 and TGF-beta.

Adoptive Transfer↗
PubMed2006

Simultaneous separation of acid and basic bioactive peptides by electrodialysis with ultrafiltration membrane.

beta-Lactoglobulin (beta-lg), one of the major whey components, can release by enzymatic hydrolysis different bioactive peptidic sequences according to the enzyme used. However, these protein hydrolysates have to be fractionated to obtain peptides in a more purified form. The aim of the present work was to evaluate the feasibility of separating peptides from a beta-lg hydrolysate using an ultrafiltration (UF) membrane stacked in an electrodialysis (ED) cell and to study the effect of pH on the migration of basic/cationic and acid/anionic peptides in the ED configuration. Electrodialysis with ultrafiltration membrane (EDUF) appeared to be a selective method of separation since amongst a total of 40 peptides in the raw hydrolysate, only 13 were recovered in the separated adjacent solutions (KCl 1 and KCl 2). Amongst these 13 migrating peptides, 3 acid/anionic peptides migrated only in one compartment (KCl 1), while 3 basic/cationic peptides migrated only in the second compartment (KCl 2) and that whatever the pH conditions of the hydrolysate solution. Furthermore, the highest migration was obtained for the ACE-inhibitory peptide beta-lg 142-148, with a value of 10.75%. The integrity of the UF membrane was kept and EDUF would minimize the fouling of UF membrane.

Animals↗
PubMed2005

Partition of whey milk proteins in aqueous two-phase systems of polyethylene glycol-phosphate as a starting point to isolate proteins expressed in transgenic milk.

Partitioning behaviour of the bovine whey proteins (bovine serum albumin, alpha lactoalbumin and beta lactoglobulin) and alpha-1 antitrypsin in aqueous two-phase systems prepared with polyethyleneglycol (molecular masses: 1000; 1500 and 3350)-potassium phosphate was analysed. Bovine serum albumin and alpha lactoalbumin concentrated in the polyethyleneglycol rich phase with a partition coefficient of 10.0 and 27.0, respectively, while beta lactoglubulin and alpha-1 antitrypsin showed affinity for the phosphate-rich phase with a partition coefficient of 0.07 and 0.01, respectively. An increase of medium pH induced an increase of the partition coefficient of these proteins while the increase in polyethyleneglycol molecular mass induced the opposite behaviour. The system polyethyleneglycol 1500-pH 6.3 showed the best capacity for recovering the alpha-1 antitrypsin with a yield of 80% and a purification factor between 1.5 and 1.8 from an artificial mixture of the milk whey proteins and alpha-1 antitrypsin. The method appears to be suitable as a starting point to isolate proteins expressed in transgenic milk.

Animals↗
PubMed2006

Hydrophobic interaction adsorption of whey proteins: effect of temperature and salt concentration and thermodynamic analysis.

The adsorptive behavior of bovine serum albumin (BSA) and beta-lactoglobulin (beta-lg) on hydrophobic adsorbent was studied at four temperatures and different salt concentrations. The Langmuir model was fitted by experimental equilibrium data showing that an increase in temperature and salt concentration results in an increase on the capacity factor of both proteins. A thermodynamic analysis coupled with isotherm measurements showed that salt concentration and temperature affected the enthalpic and entropic behavior of the adsorption process of both proteins, mainly to the beta-lg. The fast variation in the Z value for temperature over than 303.1K suggest a great conformational change occurring in the beta-lg structure, which almost duplicated the maximum adsorption capacity of this protein.

Adsorption↗
PubMed2005

Stability of thin stagnant film on a solid surface with a viscoelastic air-liquid interface.

Linear stability analysis for a film on a solid surface with a viscoelastic air-liquid interface is presented. The interfacial dilatational and shear viscoelastic properties were described by Maxwell models. Dilatational and shear interfacial elasticity and viscosity were shown to improve film stability. When the interfacial rheological properties are extremely large or small, the maximum perturbation growth coefficient is shown to reduce to those for immobile and mobile interfaces respectively. Calculated values of maximum growth coefficient for thin film stabilized by 0.5% beta-lactoglobulin approached those of mobile films for thick (>2000 nm) and those for immobile films for thin (<100 nm) films respectively with the values lying between the two limits for intermediate film thicknesses.

Air↗