Calcium Sensitivity and Molecular Weight of αs5-Casein

Abstract

Alphas5-casein was more sensitive to calcium than αs1-casein, requiring 2 mM calcium chloride for 80% protein precipitation as compared to 8 mM for αs1-casein. Ability of αs5-casein to interact with κ-casein forming micelles resistant to precipitation with calcium was less than that of αs1-casein. Molecular weights determined by the differential boundary method in an ultracentrifuge were 65,750 and 31,800 for αs5-casein and for reduced αs5-casein (the equimolar mixture of αs3- and αs4-caseins). Elution of αs5-casein at the second half of the κ-casein rich peak on Sephadex G-100 at pH 10.8 was ascribed to the molecular size of αs5-casein. © 1973, American Dairy Science Association. All rights reserved.