Purification and properties of a major casein component of rat milk.
A casein component (C2-casein) was purified by ion-exchange and gel filtration chromatography from rat milk, and the properties of this protein were examined. The molecular weight of C2-casein, as determined by Sepharose 4B gel filtration in 6 M guanidine hydrochloride, was 34 000 +/- 1000. The average hydrophobicity calculated from the amino acid composition showed that C2-casein is a rather hydrophilic protein. The alpha-helix content obtained from optical rotatory dispersion experiments was about 12%. In ultracentrifugation analyses, monomer and polymer peaks of C2-casein were both seen, and the monomer-to-polymer ratio was not affected by changing temperature conditions. C2-casein was precipitated by the presence of 2.5 mM CaCl2, and the precipitability was greatly decreased by the dephosphorylation of the protein. C2-casein was stabilized from Ca2+-dependent precipitation by the addition of another rat casein component (C3-casein) or of bovine kappa-casein.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002241:Carbohydrates / Q000032:analysis; D002364:Caseins / Q000302:isolation & purification*; D011232:Chemical Precipitation; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004355:Drug Stability; D005260:Female; D006023:Glycoproteins / Q000302:isolation & purification; D046911:Macromolecular Substances; D008892:Milk / Q000032:analysis*; D008970:Molecular Weight; D011247:Pregnancy; D011487:Protein Conformation; D051381:Rats
D000596:Amino Acids; D002241:Carbohydrates; D002364:Caseins; D006023:Glycoproteins; D046911:Macromolecular Substances