Determination of the Isoelectric Points of Casein . Due to its amphoteric nature, the solubilty of casein depends greatly on the PH of the medium. Determination of the Isoelectric Points of Casein. Certain proteins e.g. gelatin are relatively soluble in water even at their I.E.P.
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BUT maximum precipitation can be obtained at the the isoelectric point by addition of some reagents such as, ethanol which dehydrates the molecule and allow neutralization of charge.
PH = Pka + log [Sodium acetate]
Tube # 1 2 3 4 5 6 7
0.05% casein solution
in 0.1ml CH3COONa 1 1 1 1 1 1 1
Distilled Water (ml) 8.4 8 8.8 8.5 8 7 7.4
0.01M acetic acid (ml) 0.6 1 - - - - -
0.1M acetic acid (ml) - - 0.2 0.5 1 2 -
1M acetic acid (ml) - - - - - - 1.6
PK acetic acid = 4.5
PH = PKa + log [CH3COONa]
Samar A. Damiati