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  • 1
    Electronic Resource
    Electronic Resource
    Interfacial properties of tryptic peptides of .beta.-lactoglobulin (1992)
    s.l. : American Chemical Society
    Journal of agricultural and food chemistry 40 (1992), S. 669-675 
    Details
    ISSN: 1520-5118
    Source: ACS Legacy Archives
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jf00016a030
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  • 2
    Electronic Resource
    Electronic Resource
    Glycation of bovine β-Lactoglobulin: effect on the protein structure (1999)
    Oxford, UK : Blackwell Science Ltd
    International journal of food science & technology 34 (1999), S. 0 
    Details
    ISSN: 1365-2621
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Since temperature and water activity are among the most important parameters that affect the Maillard reaction, the glycation sites in pure, native bovine β-lactoglobulin were determined after a mild heat treatment (60 °C) in an aqueous solution and after a treatment under a restricted water environment (50 °C, 65% relative humidity). In both systems, the results obtained underlined the structural heterogeneity of β-lactoglobulin (β-LG) glycoforms with respect to the number of lactose residues linked per protein molecule and to the binding sites involved. Subsequently, the effect of the glycation conditions on both the association behaviour and the conformational changes of the glycated β-LG were characterised by proteolytic susceptibility, binding of the fluorescent probe 8-anilino-1-naphtalene-sulfonic acid, SDS-PAGE and size exclusion chromatography. The results showed that dry-way glycation did not significantly alter the native-like behaviour of the protein while the treatment in solution led to important structural changes. These changes resulted in a specific denatured β-LG monomer, which covalently associated via the free thiol group. The homodimers thus formed and the expanded monomers underwent subsequent aggregation to form high molecular weight species, via non–covalent interactions. The use of monoclonal antibodies with defined epitopes, raised against native β-LG, confirmed that the protein conformation was much more modified when glycation was performed in a solution while the structural changes induced during dry-way treatment were limited to the AB loop region of the protein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2621.1999.00318.x
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  • 3
    Electronic Resource
    Electronic Resource
    Apparent chemical composition of nine commercial or semi-commercial whey protein concentrates, isolates and fractions (1999)
    Oxford, UK : Blackwell Science Ltd
    International journal of food science & technology 34 (1999), S. 0 
    Details
    ISSN: 1365-2621
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Analytical results are given for whey powders prepared on a commercial or semi-commercial scale by three companies. Altogether, five preparations enriched in β-lactoglobulin, four whey protein isolates and a fraction enriched in α-lactalbumin were analyzed for protein composition, including %β-lactoglobulin, α-lactalbumin, bovine serum albumin, casein (glyco) macropeptide and the main triglycerides. Protein composition was determined by high pressure gel permeation and reversed phase liquid chromatography and by capillary zone electrophoresis. The extent of modification of the native β-lactoglobulin structure was also measured through the degree of lactosylation and the fraction of accessible free sulphydryl groups. One significant finding was that the calculated recovery of protein following quantitation of the chromatogram or electropherogram was seldom above 90% and occasionally below 60% of that loaded onto the column or capillary, raising doubts as to the reliability of the analytical results. Extrapolation by linear regression to 100% recovery allowed estimates to be made of the true β-lactoglobulin composition of the samples. The nine samples could be placed into three distinct groups with estimated true β-lactoglobulin weight % of 70.9 ± 1.1, 62.0 ± 3.4 and 39.5 ± 4.9. Physico-chemical properties of the group of samples are reported elsewhere (Holt et al., 1999).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2621.1999.00323.x
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  • 4
    Electronic Resource
    Electronic Resource
    Some physico-chemical properties of nine commercial or semi-commercial whey protein concentrates, isolates and fractions (1999)
    Oxford, UK : Blackwell Science Ltd
    International journal of food science & technology 34 (1999), S. 0 
    Details
    ISSN: 1365-2621
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The physico-chemical properties are reported for a group of whey protein powders prepared on a commercial or semi-commercial scale by three companies and chemically characterized as described elsewhere (Holt et al., 1999). The dependence of the apparent β-lactoglobulin % on the recovered % showed that the nine samples could be placed in three distinct groups with β-lactoglobulin weight % of 70.9 ± 1.1 (Group 1), 62.0 ± 3.4 (Group 2) and 39.5 ± 4.9 (Group 3). Measurements by 1H-NMR spectroscopy, on 3 of the samples confirmed that the native fold still predominated in the β-lactoglobulin. β-lactoglobulin could be crystallized from all the powders and the normal space group and cell dimensions were determined for the 8 samples that gave crystals of good enough quality for X-ray studies. Differential scanning microcalorimetry of samples dispersed in a phosphate buffer showed a clear difference between Goups 1 and 2 with a more prominent peak due to α-lactalbumin in the Group 2 samples. Light scattering and size exclusion chromatography showed that two types of aggregates were present to a variable extent in all the samples and after a heat treatment, the larger aggregates tended to predominate in Group 2. The rheology measurements, also made in the phosphate buffer, showed a difference of gel stiffness during heat treatment between the Group 1 and Group 2 samples with the exception of the BORCwpc+ sample. Within each group, gel stiffness increased with the degree of lactoslylation of the β-lactoglobulin. Interfacial measurements on samples dispersed in water presented a more complex pattern of behaviour although surface tension measurements at the air water interface of the Group 2 samples showed a two-step pattern of surface tension decrease with time, compared to a single step pattern in the Group 1 samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2621.1999.00326.x
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  • 5
    Electronic Resource
    Electronic Resource
    Induction of New Physicochemical and Functional Properties by the Glycosylation of Whey Proteins (1998)
    Springer
    The protein journal 17 (1998), S. 495-503 
    Details
    ISSN: 1573-4943
    Keywords: β-Lactoglobulin ; α-lactalbumin ; glycosylation ; functional properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nucleophilic primary amino groups of whey proteins (β-lactoglobulin and α-lactalbumin) were modified with reducing sugars in mild heat conditions. After 49 hr of heating (60°C) at pH 6.5, 20–30% of β-lactoglobulin amino groups were substituted with aldohexoses (galactose, mannose, glucose) and lactose, whereas up to 70% and 90% of β-lactoglobulin amino groups were modified with ribose and glyceraldehyde, respectively. Gel electrophoresis and reversed-phase HPLC coupled with electrospray ionization mass spectrometry of glycosylated proteins indicated that the substitution was random. Consequently, highly heterogeneous families of glycosylated proteins were generated. Proteins substituted with hexoses and lactose exhibited higher solubility and improved emulsifying properties as compared with nonglycosylated proteins, in the whole pH range studied. In contrast, proteins glycosylated with ribose and glyceraldehyde showed lower solubility close to their isoelectric points. β-Lactoglobulin modified with ribose and glyceraldehyde displayed substantial differences in denaturation behavior as compared with native protein. When compared with β-lactoglobulin, glycosylation of α-lactalbumin was quicker. There was no difference in glycosylation yields nor rates of α-lactalbumin in presence and absence of calcium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022530904218
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  • 6
    Electronic Resource
    Electronic Resource
    Soybean β-Conglycinin α Subunit is Phosphorylated on Two Distinct Serines by Protein Kinase CK2 In Vitro (1999)
    Springer
    The protein journal 18 (1999), S. 315-323 
    Details
    ISSN: 1573-4943
    Keywords: Casein kinase 2 ; protein kinase CK2 ; β-conglycinin ; electrospray ; phosphorylation sites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Protein kinase CK2 purified from the yeast Yarrowia lipolytica was used to phosphorylate soybean β-conglycinin α subunit. CK2 is known to phosphorylate serines and threonines in the consensus sequence Ser/Thr-X-X-Glu/Asp/SerP/TyrP. β-Conglycinin α subunit (68 kDa) presents seven consensus sequences, but only 0.5–1 mol P/mol α subunit was incorporated by CK2. [32P]Phosphorylated β-conglycinin α subunit was cleaved either by cyanogen bromide or by trypsin. 32P was incorporated into the largest cyanogen bromide fragment only (50 kDa, N-terminal) and only two radiolabeled zones were detected after HPLC of the trypsic digest. The corresponding phosphorylated zones were collected and further analyzed by RP-HPLC coupled to electrospray ionization mass spectrometry (LC-ESMS). Two phosphorylated sites, Ser 75 and Ser 117, were determined after MS-MS analysis of three phosphopeptides identified as 70–89, 116–126, and 116–127 sequences. Over the seven consensus sequences of β-conglycinin α subunit, Ser 75 is the only one which was phosphorylated. Ser 117 was phosphorylated although it is not an expected phosphorylation site according to the canonical consensus sequence criteria as there is no acidic determinant at the +3 position. Both Ser 75 and Ser 117 are located inside very acidic sequences, by contrast with the other unphosphorylated potential sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021091413084
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  • 7
    Electronic Resource
    Electronic Resource
    New Genetic Variants Identified in Donkey's Milk Whey Proteins (2000)
    Springer
    The protein journal 19 (2000), S. 105-116 
    Details
    ISSN: 1573-4943
    Keywords: Mass spectrometry ; protein sequence ; whey protein ; donkey milk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Novel genetic variants for donkey milk lysozyme and β-lactoglobulins I and II have been identified by the combined use of peptide mass mapping and sequencing by tandem mass spectrometry in association with database searching. The novel donkey lysozyme variant designated as lysozyme B (Mr 14,631 Da) differed in three amino acid exchanges, N49 → D, Y52 → S, and S61 → N, from the previously published sequence. Three novel genetic variants for donkey β-lactoglobulins were identified. One of them is a type β-lactoglobulin I with three amino acid exchanges at E36 → S, S97 → T, and V150 → I (β-lactoglobulin I B, Mr 18,510 Da). The two others are type β-lactoglobulins II with two amino acid exchanges at C110 → P and M118 → T (β-lactoglobulin II B, Mr 18,227 Da) and with three amino acid exchanges at D96 → E, C110 → P, and M118 → T (β-lactoglobulin II C, Mr 18,241 Da). All these primary structures are closely related to those of homologous proteins in horse milk (percent identity 〉96%).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007078415595
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