Effect of Calcium Chloride and Heat on Solutions of Mixtures of β-Lactoglobulin and Casein

Tlle effect of heat and calcium ehloride concentration on the precipitation in the ultracentrifuge of casein and /3-1aetoglobulin has been studied. With fl-lactoglobulin alone (1% solution) at pH 6.5 with 2 mM calcium chloride per liter, the protein is totally precipitated after heating at 90 for 30 rain. and ultracentrifuging (127,000 X G for 45 rain.). With ~-lactoglobulin (1%) and casein (2%) together under the same conditions, no precipitate is obtained until the calcimn chloride concentration exceeds 4 ram per liter. Eleetrophoretic examination of the supernatant solution, when 50% of the total protein is precipitated (S mM calcium chloride per liter), together with the insolubility of the precipitate in versene, suggested that the B-lactoglobulin is in the sediment. This conclusion was confirmed by the determination of the phosphorus to measure the casein distribution. Similar treatment of an unheated mixture showed that all of the B-lactoglobulin was in the supernatant solution. Also determined was the amount of calcium bound to the precipitated proteins, both alone and mixed. The total results support the assumption that the proteins in the mixture studied react independently and not as a complex.