Each protein has a point at which it can become either an acid or alkaline, that is, the neutral or isoelectric point. At this point, the protein is least soluble and will precipitate out of solution.
The pH level at which protein shows no net charge.
The pH of a protein in solution at which there are equal numbers of positive- and negative-charged groups.
The particular pH of a solution of an amphoteric electrolyte such as an amino acid or protein in which the charged molecules do not migrate to either electrode. Proteins are least soluble at this point. Thus at the appropriate pH, proteins may be precipitated.