Fractionation of bovine caseins by reverse phase high performance liquid chromatography: identification of a genetic variant

Mammary transcriptome analysis of lactating dairy cows following administration of bovine growth hormone

The galactopoietic effect of growth hormone (GH) in lactating ruminants is well established; however the mechanisms that mediate these effects are not well understood. The first objective of this study was to determine the effect of GH on the synthesis of the major casein and whey proteins. The second objective was to identify the genes and pathways that may be involved in mediating the effect of GH on milk synthesis. A single subcutaneous injection of a commercially available slow release formulation of GH (Lactatropin®), or physiological saline solution (control) was administered to non-pregnant dairy cows (n=4/group) in mid-late lactation. Milk samples were collected for composition analysis and mammary lobulo-alveolar tissue was collected postmortem 6 days post injection. Gene expression profiles were evaluated using either a 22 000 bovine complementary DNA microarray or quantitative PCR (qPCR), and microarrays were validated by qPCR. The yield of all the major casein and whey proteins was increased 32% to 41% in GH-treated cows, with the exception of α-lactalbumin yield which was elevated by 70% relative to controls. Treatment with GH treatment tended to increase the concentration of α-lactalbumin but had no effect on the concentration of any of the major milk proteins. Messenger RNA (mRNA) abundance of the major whey and casein genes, with the exception of α-s2-casein, was increased in response to GH compared with controls, which is consistent with the positive effect of GH on milk production. Treatment with GH treatment influenced the mRNA abundance of genes involved in cell growth and proliferation, transcriptional and translational regulation, actin cytoskeleton signalling, lipid metabolism and cell death. This study has provided new insights into the cell signalling that may be involved in mediating the effect of GH on milk production in the mammary gland of lactating dairy cows.

Identification of a new genetic variant of bovine beta-casein using reversed-phase high-performance liquid chromatography and mass spectrometric analysis

Various components of the beta-casein fraction from bovine milk were separated by preparative reversed-phase high-performance liquid chromatography (RP-HPLC). They included the genetic variants beta A1, beta A2, beta A3, and an unknown component previously denoted beta X [S. Visser et al., J. Chromatogr. 548 (1991) 361-370]. Tryptic digests of these components were compared by RP-HPLC and most peaks were analysed by mass spectrometry (MS). The tryptic map of beta X was closest to that of beta A1, but with a few mutually different peak components. Electrospray ionisation MS revealed that in the beta X map these components had relative molecular masses of 16 higher than the corresponding ones in the beta A1 map. The main differential peaks represented the 114-169 fragments of beta A1 and beta X, respectively, which were both purified and then cleaved with cyanogen bromide. In the resulting mixtures, each of which contained three fragments, the corresponding peptides representing the 145-156 sequence showed the 16 relative molecular mass difference. In beta X this sequence contained a Leu residue at position 152 instead of the Pro-152 in beta A1, as established by fast-atom bombardment MS-MS. The Leu could be discriminated from an Ile residue by the presence of a side-chain-specific, D-type fragment ion in the MS-MS spectrum of the beta X CNBr peptide. The sequence of the two homologous 145-156 fragments was confirmed by regular amino acid sequence analysis. In accordance with internationally accepted guidelines for the nomenclature of milk proteins, the new genetic variant has been named beta-casein F-5P.

Chromatographic and electrophoretic methods used for analysis of milk proteins

Current knowledge of milk proteins and their behavior in dairy foods is based on early applications of chromatography and electrophoresis. Electrophoretic identification of the number and genetic variety of milk proteins inaugurated a research effort in which chromatographic techniques were successfully applied to the isolation of each milk protein, thus facilitating the characterization and further study of milk and dairy products. This review focuses on recent applications of chromatography for separations and analysis and on analytical applications of electrophoresis.

Separation of beta-casein A1, A2, and B using cation-exchange fast protein liquid chromatography

beta-Casein genetic variants A1, A2, and B were separated using cation-exchange fast protein liquid chromatography. beta-Casein from a herd bulk casein sample eluted as a series of three peaks. Casein samples from individual cows containing known combinations of beta-casein A1, A2, and B were used to confirm that the three peaks were beta-casein genetic variants. An acid-PAGE gel confirmed the identity of the peaks that eluted from the column.

Quantification of alpha s1-casein in goat milk from French-Alpine and Anglo-Nubian breeds using reversed-phase high performance liquid chromatography

Samples of isoelectrically precipitated goat casein from the milks of French-Alpine and Anglo-Nubian breeds were separated into four components in a single run by reversed-phase HPLC. The proportion of alpha s1-casein thus resolved was determined quantitatively. The method uses a reversed-phase C-4 column and a linear gradient from 30 to 50% acetonitrile in 30 min with trifluoroacetic acid constant at .1%. Sodium dodecyl sulfate-PAGE was carried out to establish the identity of the isolated components. By a comparison with previously published results for caprine and bovine milk caseins, the four peaks were identified as kappa-, alpha s2-, alpha s1-, and beta-casein. Quantitative variations in the chromatographically resolved alpha s1-casein fraction of goat milk were evident. Some individual goat milks contained high levels of alpha s1-casein (2.70 g/L), but others contained significantly low levels (.12 g/L). There was no statistical difference in the overall means between breeds in alpha s1-casein composition, but cluster analysis statistics showed three distinct categories of alpha s1-producers: high, medium, and low. Interestingly, 6 of 15 French-Alpine goats and only one Anglo-Nubian goat fell into the "low" producer category (.38 +/- .2 g/L). Thus, expression of the alpha s1-component may be genetically regulated but may not be a breed-specific trait.

Phenotyping of bovine milk proteins by reversed-phase high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic method for the separation of the most common and some less common genetic variants of the bovine caseins is described. When the method is used for analysing clarified skim milk, simultaneous identification of casein variants and major they protein variants can be effected in a single run. The potential of the method for quantitative application is discussed.

Analysis of tryptic digests of bovine beta-casein by reversed-phase high-performance liquid chromatography

Reversed-phase high-performance liquid chromatography (RP-HPLC) was used to separate the tryptic peptides of beta-casein. A gradient of 0-50% acetonitrile in 0.1% trifluoroacetic acid at a flow-rate of 0.8 ml/min resolved ten of the thirteen peptides. A modified gradient resolved the three peptides eluted at ca. 25% acetonitrile. RP-HPLC proved superior to high-voltage paper electrophoresis in analysis time, resolution and flexibility. The methods developed for the analysis of proteolysis of the milk protein, beta-casein, are now being applied to study the action of extracellular proteases from dairy bacteria on milk proteins.

Hydrophobic interaction fast protein liquid chromatography of milk proteins

Bovine whey proteins and caseins were separated by hydrophobic interaction chromatography with the new Pharmacia fast protein liquid chromatography column, phenyl-Superose. Total casein was separated using a decreasing gradient of 0.8 to 0.05 M sodium phosphate and a constant 3.75 M urea concentration at pH 6.0. The order of elution of caseins was beta less than gamma, alpha s2 less than kappa less than alpha s1, and beta-casein was always eluted first. Whey proteins were separated with a decreasing salt gradient of 1.5 to 0 M ammonium sulphate in 0.05 M sodium phosphate at pH 7.0. The order of elution was beta-lactoglobulin less than bovine serum albumin less than immunoglobulin less than alpha-lactalbumin. The elution order of proteins from the column did not correlate with the calculated average hydrophobicities but the method was considered to be a measure of the "effective" hydrophobicity of proteins and therefore of more use for attempting to relate hydrophobicity to functional properties of proteins. The method shows significant advantages over conventional techniques allowing rapid optimization of elution conditions and reducing run times from 24 h or more to less than 2 h.