DETERMINATION OF ISOELECTRIC POINTS OF ACIDIC AND BASIC-PROTEINS BY CAPILLARY ELECTROPHORESIS

The isoelectric point (pi) of a protein is of practical importance in many separation procedures, both analytical and preparative. The pi is defined as the pH where the net charge of the protein is zero. Therefore, by plotting the mobilities of the proteins against pH, the intercept at zero mobility should yield the pi value. Isoelectric points have traditionally been determined by isoelectric focusing. In this paper, the potential of capillary electrophoresis as an alternative technique for the determination of pI values of both acidic and basic proteins was investigated. The problem commonly encountered with adsorption of the positively charged proteins with the unprotonated silanol groups of the fused-silica wall is solved by applying a dynamic coating of a polycationic reagent to the wall. The advantages of this technique of determining the pI values are simplicity, speed and minimal sample requirement.