| Popis: |
In order to explain the higher calcium sensitivity of α s2 -casein than other casein constituients, properties of α s2 -casein and dephosphorylated α s2 -casein were examined and compared with those of α s1 -casein. α s2 -Casein was more sensitive to calcium than α s1 -casein. Aggregates of calcium α s1 - and α s2 -caseinates were both thoroughly solubilized by 4 M urea. Gel filtration of α s1 -casein and of α s2 -casein in 4 M urea showed the same elution pattern in the presence and absence of 10m M calcium chloride. Dephosphorylated α s2 -casein was insoluble at neutral pH although dephosphorylated α s1 -casein was soluble. Dephosphorylated α s2 -casein was solubilized by 4 M urea and alkalization to pH 11. The net proton charge, calculated from the primary structure, of dephosphorylated α s2 -casein was very low at pH 7.0, although dephosphorylated α s1 -casein has a considerable number of negative net charges. The calculated isoionic point of dephosphorylated α s2 -casein, which contains one phosphate group, was 6.98. Ester phosphate groups of α s2 -casein play an important role in its solubilization at neutral pH and neutralization of ionized phosphate groups by calcium ion increases hydrophobic interaction, which leads to precipitation. |
