Preparation of Calcium-Sensitive α-Casein

Abstract

A relatively simple modification of the method for fractionating whole casein in urea solutions is described which gives Ca-sensitive [alpha]-casein. The yield is about 40% of total [alpha]-casein. This casein and [alpha]-paracasein precipitate to the same extent with CaCl2; 10 m[image] CaC/liter at pH 7 is sufficient to precipitate a 1% solution of each casein. The 2 caseins can, however, be distinguished by their initial rates of aggregation with lower concentrations of CaCl2 (1.5 to 3.5 m[image]/ liter. With low concentrations of CaCl2, whole [alpha]-casein aggregates to a greater extent than does Ca-sensitive [alpha]-casein. The Ca-sensitive [alpha]-casein appears to be homogeneous on electrophoresis at pH 8.5 and 2.3. Very little (less than 1%) of this casein is made soluble by the action of rennin.