Β-casein Fraction Research Articles

Isolation of Canine αs-Casein and Major Whey Protein Component A and Their Amino Acid Composition

Canine whole casein shows two strong bands designated “Canine αs- and β-casein” corresponding to bovine αs- and β-casein on gel electrophoresis, but both αs- and β-casein have lower mobilities than bovine counterparts. Canine αs-casein was isolated by column chromatography on DEAE cellulose, whereas canine β-casein fraction was isolated by urea fractionation. Phosphorus content and calcium sensitivity of the canine αs-casein and β-casein fraction resemble those of bovine αs- and β-casein, espectively. Canine αs-casein contains more arginine and less serine, glycine, methionine and lysine. Canine β-casein fraction has a high nonpolar amino acid as bovine β-casein, but it is low in glycine and tryptophan. Canine whey protein has five major bands on gel electrophoresis. Major Component A, the fastest moving band has greater mobility than bovine β-lactoglobulin. Component A was isolated by salt fractionation and by column chromatography on DEAE cellulose. Amino acid composition of Component A resembles that of bovine β-lactoglobulin, with less lysine and more arginine in the former. Also it resembles that of porcine β-lactoglobulin, with less serine and lysine and more tyrosine and tryptophan in the former.

Polymorphism of Whey2 Protein of Sow's Milk

Polyacrylamide vertical gel electrophoresis was used to separate an unidentified whey protein variant of sow's milk. The protein which migrates to the area directly below the β-casein fraction of sow's milk was identified as the whey2 region. The proposed polymorphism appears to be controlled by three codominant alleles labelled Whey2A, Whey2B, and Whey2C, each corresponding to a separate zone within the whey2 region. Allele A was designated as the fastest migrating, B intermediate, and C the slowest zone. The electrophoretic analysis shows that each allele gives rise to three protein bands, similar to the transferrins in pig serum. After electrophoresis, the homozygous condition appears as a single zone within the whey2 region comprised of three bands. The heterozygous condition appears as a combination of two zones within the whey2 region comprised of six bands. A total of six phenotypes is possible and each has been found. Further family studies will be necessary to confirm genetic control of this whey2 protein polymorphism.

Growth of Selected Bacteria in Liquid Media Containing DDT, Dieldrin and Heptachlor

Growth of Pseudomonas fluorescens and Staphylococcus aureus in trypticase soy broth was affected by DDT exceeding 50μg per milliliter. This effect was more pronounced after the first day of incubation. No effect on growth was observed in skimmilk containing up to 100μg per milliliter of DDT.Concentration of 3μg per milliliter of heptachlor in trypticase soy broth inhibited the growth of S. aureus up to 18 hours, whereas 15 to 20μg per milliliter prevented growth up to 7 days. Inhibition of S. aureus was not observed in skimmilk or in trypticase soy broth plus 3% whole casein or mixture of α- and β-casein fraction containing up to 100μg per milliliter of heptachlor. Heptachlor epoxide had no inhibitory effect, whereas 72% heptachlor was more inhibitory than 99% heptachlor.

Glycosidases in bovine milk: alpha-mannosidase and its inhibition by zwitterions.

α-Mannosidase is present in bovine milk and is associated with the β-casein fraction following polyacrylamide gel electrophoresis. It was separated from the casein complex by ammonium sulfate precipitation in the presence of 10% (v/v) ethanol. Zinc or manganese ions are required for maximum activity and the enzyme is very labile. The optimum pH for the hydrolysis of p-nitrophenyl α-mannoside is about 3. In the presence of amino acid buffers the enzyme is inhibited. For dibasic amino acids this inhibition is inversely related to the [Formula: see text] of the amino acid and is apparently due to inhibition by zwitterions. High concentrations of the substrate p-nitrophenyl α-mannoside are inhibitory, and the apparent Km for this hydrolysis is 1.2 mM.

Turbidimetric Behavior of Casein Fractions after Treatment with Rennet

Pure κ-casein solutions in concentrations of less than 0.1% produce measurable turbidities in acetate buffer in the presence of dilute rennet solutions at pH 5.8 and 30C. In mixtures of αs- and κ-casein containing less than 20% κ- the increase in turbidity after 5min is proportional to the percentage κ-casein in the mixture. Calcium is needed in the reaction mixture (.008M) to bring about the turbidity increases. The turbidity of pure αs-casein is not affected by addition of rennet. Variable increases in turbidity after rennet action on purified β-casein fraction point to the difficulty of separation of κ-casein from β-casein. Isolated whole casein reacts more slowly with rennet than does purifled κ -casein.

Non-independent Occurrence of αS1 and β-Casein Variants of Cow's Milk

THE β-casein fraction of cow's milk has been found to show genetic variants distinguishable by electrophoresis1. Part of the αs-casein fraction, now called αs1-casein (ref. 2), also shows genetic variation3. The αS1-casein type B and the β-casein type A are prevalent, while the other two known variants of each only occur in some breeds of cattle4,5. In Jersey cows αS1-casein type C and β-casein type B are seen in a fair proportion of cases.

Preparation of β-casein by a modified urea fractionation method

It has been shown by Hipp, Groves, Custer & McMeekin (1952) that the differential solubility in urea of the casein components of cow's milk can be utilized for preparative purposes. Fractionation is achieved by step-wise dilution of a solution of all the casein components in strong (6·6 molar) urea. In connexion with the work on the three genetically distinct β-caseins discussed in the preceding paper, the need arose to prepare the variants A, B and C from the milk of appropriate homozygotes. This led to the development of the modified procedure described in this note, a procedure more sparing in urea and more effective in the initial isolation of the β-casein fraction than the original method of Hipp et al.