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PubMed1986

beta-Lactoglobulin and alpha-lactalbumin in mammary secretions during the dry period: parallelism of concentration changes.

Proteins in mammary secretions were examined during the dry period of four cows. Polyacrylamide gel electrophoresis was used to determine relative changes in the electrophoretic profiles of whey proteins in the mammary secretions. Concentrations of beta-lactoglobulin and alpha-lactalbumin in dry cow secretions were determined by immunoassay. Concentrations of both proteins changed in parallel during the dry period. Concentrations of beta-lactoglobulin and alpha-lactalbumin decreased during the first 30 d of the dry period but generally remained above .1 mg/ml secretion. A transient increase in beta-lactoglobulin and alpha-lactalbumin concentrations occurred at about 40 d after drying-off, prior to the prepartum increase.

Animals↗

PubMed1992

Chromosome substitution effects associated with kappa-casein and beta-lactoglobulin in Holstein cattle.

Allelic variants of kappa-casein and beta-lactoglobulin were used to estimate chromosome substitution effects on transmitting abilities for yield traits among sons of two Holstein sires. Sire 1 was a heterozygote for both loci, whereas sire 2 was a heterozygote for beta-lactoglobulin only. Transmitting abilities for fat percentage and the exchange of protein and fat (protein yield minus fat yield) were influenced by kappa-casein genotype among offspring of sire 1. The B allele of kappa-casein was associated with a decrease in fat percentage, whereas fat yield was not affected; the result was 4.5 kg more transmitting ability for protein than for fat. Favorable chromosome substitution effects on transmitting abilities for fat percentage, protein yield, and the exchange of protein and fat were also observed for the A allele of beta-lactoglobulin among offspring of sire 1; there were consistent but not significant estimates for sire 2. These results suggest that different estimates could be obtained from offspring of different parents, perhaps from linkage disequilibrium between families. The chromosome substitution effects appeared to be in the direction opposite to the average correlation of milk fat and protein content; marker-assisted selection for increased yield of protein would result in decreased fat yield.

Alleles↗

PubMed1976

[Antibrucellosis lactoglobulin and a study of its therapeutic action under experimental conditions].

Antibrucellosis lactoglobulin obtained by the author had higher specific antibody titres (1 : 81920) than the gamma-globulin batches prepared earlier from the bovine blood serum (1 : 3200). The suggested antibrucellosis lactoglobulin was harmless, of low reactogenicity and produced a definite therapeutic action when administrated to the infected animals. Since lactoglobulin is less expensive than gamma-globulin further work on the improvement of technology of obtaining the former and on the elaboration of the most effective schemes of its use are of expedience.

Animals↗

PubMed1979

Immunological evidence of beta-lactoglobulins in human colostrum and milk.

Over thirty specimens of breast milk and colostrum were examined by the double diffusion method in agarose gel using antibovine beta-lactoglobulin antisera. Cross reactions were obtained showing the presence of beta-lactoglobulins in human milk and colostrum; the strength of these reactions was comparable with those already observed with porcine and equine mammary secretions. Identity reactions were obtained between human and sow's milk against anti-bovine beta-lactoglobulin antisera. Results are discussed from the immunological and structural point of view.

Animals↗

PubMedDate not supplied

[Calorimetric study of the thermal denaturation of beta-lactoglobulin in the presence of urea and phosphate ions].

The denaturation of beta-lactoglobulin in solution with different content of urea and phosphates has been studied calorimetrically. It has been shown that the increase of phosphate ion concentration in solution leads to an increase of beta-lactoglobulin stability, while increase of urea concentration leads to an opposite effect. The variation of these components in solution practically does not influence the value of the heat capacity increment of beta-lactoglobulin in the considered temperature region. Accordingly the denaturation enthalpy is a linear function of temperature whose slope does not differ for solution with urea concentration less than 4.4 M. However, the absolute value of denaturation enthalpy in these solutions at corresponding temperatures differs significantly due to the heat effect of additional urea solvation during transition to the denatured state. The latter leads to a decrease of the overall denaturation enthalpy and, as a result, a shift of the enthalpy plot to higher temperatures providing conditions for studying the thermodynamic and structural characteristics of the molecule in the cold denatured-state.

Anions↗

PubMed1975

ESR study of aqueous dispersions of beta-lactoglobulin and spin-labelled glyceryl monostearate.

From the ESR spectra of aqueous dispersions of synthetic glyceryl monostearate (spin labelled at C-12) a critical micelle concentration of 30 mumol/l at room temperature was obtained, which agrees with that deduced from surface tension measurements. At monoglyceride concentrations smaller or larger than the critical micelle concentration, the monomers show increased motional restriction with increasing molar ratio of beta-lactoglobulin to monoglyceride up to a value of 10, as determined from calculated rotational correlation times; A similar progressive interaction was deduced from spectral changes observed on equimolar dispersions of beta-lactoglobulin and monoglyceride on raising the temperature to 55 degrees C at which the protein and monoglyceride coprecipitate. The relevance of these finding for non-labelled monoglyceride dispersions is indicated by the similarity of the pH-dependent flocculation behaviour of labelled and non-labelled monoglycerides, both in the absence and presence of beta-lactoglobulin; In addition, proton magnetic resonance and mechanical stability measurements suggest that spin-labelled glyceryl monosterate behaves analogously to non-labelled glyceryl monooleate.

Binding Sites↗

PubMed1996

Structural changes of beta-lactoglobulin B induced by urea. Evidence of residual structure.

Several spectroscopic methods have been used to study the structure of beta-lactoglobulin B at pH 2.1 in the presence of 8M urea. Fluorescence and polarization of fluorescence spectroscopy measurements indicate that the two tryptophanyl residues of the protein are exposed to the solvent in the denatured state. CD in the far-UV indicates that the amount of secondary structure in the denatured state is comparable to that found in the native state, whereas the CD spectrum in the near-UV shows that the tertiary structure is not completely disordered. The results of one-dimensional 1H NMR spectroscopy show that some local non-random structure is maintained in the denatured state, but most of the polypeptide chain has an extended non-globular conformation under the conditions of the present experiments. This conclusion is reinforced by the results of two-dimensional 1H NMR conducted on denatured samples of beta-lactoglobulin B. The study of states with intermediate levels of order will aid the understanding of how the native structure of beta-lactoglobulin B is organised during the refolding pathways.

Animals↗

PubMed1998

Evidence for a common epitope between bovine alpha-lactalbumin and beta-lactoglobulin.

The aim of this work was to check and quantify any cross-reactivities among the main bovine whey proteins, utilizing purified polyclonal antibodies against bovine beta-lactoglobulin, alpha-lactalbumin and serum albumin, and to identify possible common epitope(s). Purified polyclonal anti-bovine beta-lactoglobulin antibodies show 10% cross-reactivity with bovine alpha-lactalbumin, both in its native and its denatured form. A continuous stretch of four amino acids common to alpha-lactalbumin and beta-lactoglobulin that might be responsible for this cross-reactivity has been identified. Cross-reactivity between this antibody and bovine serum albumin is, on the contrary, negligible. Purified polyclonal anti-bovine alpha-lactalbumin and anti-serum albumin antibodies do not cross-react.

Amino Acid Sequence↗

PubMed1999

Detergent-Induced Removal of beta-Lactoglobulin from Stainless Steel Surfaces as Influenced by Surface Pretreatment.

The adsorption of beta-lactoglobulin to stainless steel and its subsequent removal were followed using in situ null ellipsometry. The influence of the surface pretreatment on the protein removal by the surfactant SDS and by sodium hydroxide was studied. All surfaces were precleaned in strongly alkaline solution. Some surfaces received no further pretreatment, while others were either passivated in nitric acid or plasma-cleaned prior to experiments. Stainless steel surfaces subjected to different surface pretreatments showed considerable differences in cleaning behavior. Cleaning, using NaOH, of surfaces which had been precleaned with alkali only or with plasma resulted in practically complete beta-lactoglobulin removal. In contrast, appreciable amounts of protein remained on passivated stainless steel. Protein removal by SDS was limited and comparable for all three surface pretreatments investigated. Only minor effects on the protein adsorption tendency were observed. The amounts of beta-lactoglobulin adsorbed tended to be somewhat lower on the passivated surfaces. Copyright 1999 Academic Press.

Journal Article↗

PubMed2000

Interfacial Behavior of beta-Lactoglobulin at a Stainless Steel Surface: An Electrochemical Impedance Spectroscopy Study.

The electrochemical impedance spectroscopy technique was used to investigate the interfacial behavior of beta-lactoglobulin at an austenitic stainless steel surface over the temperature range 299 to 343 K at an open circuit potential. The electrode/electrolyte interface and corresponding surface processes were successfully modeled by applying an equivalent-electrical-circuit approach. A charge-transfer resistance value was found to be very sensitive to the amount of adsorbed protein (surface concentration), thus indicating that the adsorption of the protein (i) was accompanied by the transfer of the charge, via chemisorption, and (ii) influenced the mechanism and kinetics of the corrosion reaction. This was also apparent from the large decrease in the corrosion activation energy (16 kJ mol(-1)) caused by the adsorption of the protein. Adsorption of beta-lactoglobulin onto the stainless steel surface at an open circuit potential resulted in a unimodal isotherm at all the temperatures studied and the adsorption process was described with a Langmuir adsorption isotherm. From the calculated Gibbs free energies of adsorption it was confirmed that beta-lactoglobulin molecules adsorb strongly onto the stainless steel surface. The enthalpy and entropy values indicated that the molecule partially unfolds at the surface upon adsorption. The adsorption process was found to be entirely governed by the change in entropy. Copyright 2000 Academic Press.

Journal Article↗

PubMed1998

Thiol Reactivity in Pressure-Unfolded beta-Lactoglobulin. Antioxidative Properties and Thermal Refolding.

Pressure treatment of beta-lactoglobulin (0.11 mM in aqueous 0.16 M NaCl, pH 7.61, at 15 degrees C for 30 min, up to 400 MPa investigated) induces antioxidative properties as shown for linoleic acid peroxidation in oil-in-water emulsions. The antioxidative properties obtained through pressure treatment are gradually lost at ambient pressure and paralleled by a decrease in thiol exposure and reactivity, as determined with Ellman's reagent, in an entropy-controlled (DeltaS() = -247 +/- 7 J mol(-)(1) K(-)(1)) first-order renaturation process (half-life of 3.1 h at 25 degrees C, pH 7.61, independent of pressure used for denaturation at least up to 250 MPa) with a modest temperature dependence (DeltaH() = 23 +/- 2 kJ mol(-)(1)). The reactivity of the thiol group toward Ellman's reagent was studied kinetically by stopped-flow spectrometry. The apparent second-order rate constant for this reaction at pH 7.61 and 25 degrees C changes from 5.7 x 10(2) L mol(-)(1) s(-)(1) for native beta-lactoglobulin to 1.6 x 10(5) L mol(-)(1) s(-)(1) for beta-lactoglobulin pressure-denatured at 200 MPa. Half-denaturation occurred at approximately 50 MPa. The degree of exposure of the thiol group corresponds to half-denaturation around approximately 140 MPa with a reaction volume, DeltaV degrees, for denaturation of -61 +/- 3 mL.mol(-)(1), a difference in half-denaturation pressure which may indicate that pressure denaturation is a stepwise process.

Journal Article↗

PubMed2002

Limited conformational change of beta-lactoglobulin when adsorbed at the air-water interface.

Detailed insight can be obtained from proteins at and near the air-water interface using external reflection IR and circular dichroism techniques. Besides information on local protein concentrations and surface layer thickness, it is shown that beta-lactoglobulin displays a limited unfolding at the interface. The conformational change is comparable to that observed upon heat-induced aggregation of the protein and can be understood in view of the high surface concentration of the protein (approximately 40% volume fraction). The layer thickness and the conformational properties of the protein do not depend on the bulk concentration. After adsorption of beta-lactoglobulin to a preformed lipid monomolecular layer a similar conformational change is induced, suggesting that the folding properties of the protein itself determine the extent of conformational changes at the interfaces.

Adsorption↗

PubMed2006

Investigating the permanent electric dipole moment of beta-lactoglobulin fibrils, using transient electric birefringence.

Amyloid fibrils, which are polymeric assemblies of protein molecules, have been intensively studied on a structural level, yet due to complications such as the disorder within the molecules, several aspects of their structure remain mysterious. Similarly, the kinetics of assembly are not well understood. Here we investigate the electric dipole moment of beta-lactoglobulin fibrils, a model amyloid fibril system, by applying the technique of transient electric birefringence. This moment appears to be large, and comparable to the total moment of the constituent protein monomers if they were joined in a chain, head-to-tail, without changing conformation, suggesting an ordered joining of monomers in the fibril. Such an ordered assembly may have implications for the assembly mechanism of beta-lactoglobulin fibrils in particular, and amyloid fibrils in general.

Amyloid↗

PubMed2003

Separation of alpha-lactalbumin and beta-lactoglobulin using membrane ultrafiltration.

There is considerable commercial interest in the preparation of individual whey proteins as high-value food additives, nutraceuticals, and therapeutics. This study examined the use of membrane filtration for the separation of alpha-lactalbumin and beta-lactoglobulin. Stirred cell filtration experiments were performed using both cellulosic and polyethersulfone membranes to determine the optimal pH, ionic strength, and filtration conditions. Selectivities of greater than 55 could be achieved at pH 5.5 and 50 mM ionic strength using a 30-kD cellulose membrane. A diafiltration process was then designed for the protein separation. A 16-diavolume filtration yielded beta-lactoglobulin as the retentate product with a purification factor of 100 and recovery of 90%. The alpha-lactalbumin was recovered in the filtrate with a purification factor of more than 10 and nearly 99% yield. Model calculations were in good agreement with the experimental data.

Cellulose↗

PubMed1997

Cooperative alpha-helix formation of beta-lactoglobulin and melittin induced by hexafluoroisopropanol.

Alcohols denature the native state of proteins, and also stabilize the alpha-helical conformation in unfolded proteins and peptides. Among various alcohols, trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP) are often used because of their high potential to induce such effects. However, the reason why TFE and HFIP are more effective than other alcohols is unknown. Using CD, we studied the effects of TFE and HFIP as well as reference alcohols, i.e., methanol, ethanol, and isopropanol, on the conformation of bovine beta-lactoglobulin and the bee venom melittin at pH 2. Upon addition of alcohols, beta-lactoglobulin exhibited a transformation from the native state, consisting of beta-sheets, to the alpha-helical state, whereas melittin folded from the unfolded state to the alpha-helical state. In both cases, the order of effectiveness of alcohols was shown to be: HFIP > TFE > isopropanol > ethanol > methanol. The alcohol-induced transitions were analyzed assuming a two-state mechanism to obtain the m value, a measure of the dependence of the free energy change on alcohol concentration. Comparison of the m values indicates that the high potential of TFE can be explained by the additive contribution of constituent groups, i.e., F atoms and alkyl group. On the other hand, the high potential of HFIP is more than that expected from the additive effects, suggesting that the cooperative formation of micelle-like clusters of HFIP is important.

1-Propanol↗

PubMed1998

Mapping fatty acid binding to beta-lactoglobulin: Ligand binding is restricted by modification of Cys 121.

Native beta-lactoglobulin (Blg) binds 1 mole of palmitic acid per mole of protein with a dissociation constant of 0.6 microM for the primary fatty acid binding site. Chemical modification of Cys 121, which lies at the external putative hydrophobic binding site of Blg, does not affect retinol or 4,4'-bis 1-(phenylamino)-8-naphthalenesulfonate (bis-ANS) binding to the protein, indicating that the incorporated appendages do not perturb the internal hydrophobic site within the beta-barrel of Blg (i.e., the retinoid site is unaffected). On the other hand, methylation of Cys 121, reduces the affinity of Blg for palmitic acid by 10-fold as monitored by intrinsic fluorescence. Modification of the Cys 121 with methylmethanethiosulfonate or a thiol-specific spin label appears to either further weaken or totally eliminate fatty acid binding, respectively, due to steric hindrance. Furthermore, this binding pattern has been independently verified using a spin labeled fatty acid analog and monitoring ESR as well as by bis-ANS fluorescence when bound to the protein. These results suggest that fatty acids bind at the "external site" of beta-lactoglobulin, between the sole alpha-helix and the beta-barrel. In addition, structural stability studies of native and chemically modified Blg appear to confirm this observation as well.

Anilino Naphthalenesulfonates↗

PubMed2002

Construction and characterization of beta-lactoglobulin chimeras.

At neutral pH, equine beta-lactoglobulin (ELG) is monomeric, whereas bovine beta-lactoglobulin (BLG) exists as a dimer. To understand the difference in the oligomerization properties between ELG and BLG, three mutants of ELG (LP, I, and LPI) were constructed by substituting amino acids responsible for important interactions at the dimer interface of BLG into ELG. The mutant LP has an AB loop mutation (S34A/E35Q), the mutant I has an I strand mutation (G145M/R146H/V147I/Q148R/I149L/V150S/P151F/D152N/L153P) and the mutant LPI includes both the LP and I mutations. The far- and near-UV CD spectra of the three mutants are similar to that of the wild-type ELG, indicating that the secondary and the tertiary structures of ELG are not significantly affected by the mutations. Ultracentrifuge analysis shows that all three mutants are monomeric at neutral pH, suggesting that the protein sequences in the AB loop and I strand of BLG alone cannot support dimerization of ELG. Thus, structural differences must exist between ELG and BLG that prevent the ELG mutants from forming the same interactions as BLG at the dimer interface.

Amino Acid Sequence↗

PubMed2001

Identification of novel hypocholesterolemic peptides derived from bovine milk beta-lactoglobulin.

This study was designed to clarify the mechanisms of hypocholesterolemic action of beta-lactoglobuline tryptic hydrolysate (LTH) and to identify the novel hypocholesterolemic peptide derived from LTH by screening using Caco-2 cells and animal studies. Serum and liver cholesterol levels were significantly lower in rats fed LTH than in those fed casein tryptic hydrolysate (CTH). The present study suggests that the inhibition of micellar solubility of cholesterol which causes the suppression of cholesterol absorption by a direct interaction between cholesterol mixed micelles, and LTH in the jejunal epithelia is part of the mechanism underlying the hypocholesterolemic action of LTH. Though no one could trace the hypocholesterolemic peptide to any protein origin, we identified, for the first time, a novel hypocholesterolemic peptide, Ile-Ile-Ala-Glu-Lys (IIAEK). Surprisingly, the present study provides the first direct evidence that a new hypocholesterolemic peptide derived from beta-lactoglobuline can powerfully influence serum cholesterol levels and exhibit a greater hypocholesterolemic activity in comparison with that of medicine, beta-sitosterol, in animal studies.

Administration, Oral↗