The two ends are connected to a voltage source, a battery, and the proteins are placed into our gel. Now, each protein will move due to the presence of an electric field as a result of that battery source. And so when they reach their pi value, the isoelectric point, they will stop moving because the net charge at the pi value of the protein is zero. Now, of course, this method is not very useful if these three proteins have the same combination, have the same number of these ionizable amino acids, because what that means is these three proteins will have the same exact value for the isoelectric point. So they have to have a different isoelric point value for this technique to actually be useful in separating our proteins. Now, the question is, how exactly do you determine what your pi value is for a specific polypeptide?