Using BIACORE as Pots and Pans
What would you do if you wanted to know the approximate isoelectric point of a protein? I was reluctant to run isoelectric point electrophoresis, so I tried it on BIACORE instead. In principle, a protein is positively charged when dissolved in solution at a pH below its isoelectric point, and it will be absorbed to negatively charged CM dextran. This is basically how ligand is concentrated on the dextran matrix when it is immobilized. I lowered the pH of a sample solution gradually, and a protein began to absorb to the sensor chip at a certain pH label which represents the isoelectric point of the protein. In one example, a protein was not absorbed to the sensor surface at pH 5 at all, but was absorbed at pH 4.5 (see figure), indicating that its isoelectric point was between pH 4 and 5. Later, I had a chance to run the capillary isoelectric point electrophoresis and confirmed it was actually a pi of 4.5.