Isolation and some properties of bovine [gamma]-casein

Abstract

The utilization of calcium phosphate gel for the development of a batch-type procedure for the isolation of bovine Y-casein was investigated. Preparation of crude whole Y-casein was based upon the differential solubility of the major casein fractions in aqueous urea solutions. This preparation contained approximately 62% B-casein, 32% Y-casein, 3% of the temperature-sensitive caseins, and a small amount of unidentified material. The crude whole Y-casein was dissolved to a final concentration of 2% in a 0.02 M potassium phosphate buffer, pH 6.8, containing 4.5 M urea and 0.005 M KCl. B-casein contamination was progressively removed by five successive calcium phosphate gel treatments (1.5 g gel/g protein). However, several variations of this procedure failed to remove the contamination resulting from the presence of the temperature-sensitive caseins. The final product contained 94.8% Y-casein and was devoid of any major casein fractions. However, since this preparation contained 5.2% temperature-sensitive casein, it was properly labelled whole Y-casein. A yield of approximately 15% of the whole Y-casein present in whole casein could be recovered with this procedure. The solubility of whole Y-casein in citrate-phosphate buffer (pH 4.0-6.5) decreased with increasing temperature (5, 15, and 25 C). At all three temperatures, the solubility decreased with decreasing pH toward a minimum near the isoelectric point of whole casein..