Isoelectric points of proteins: Theoretical determination

Three methods for calculating the isoelectric points (pI) of proteins, provided that their amino acid compositions are known, are described. The comprehensive and abridged procedures involve solutions of polynomial equations of different degrees depending on whether pK values of the specific acid-base residues or the means of some of those values, respectively, are adopted. In the simplified procedure, approximate pI values of proteins can be determined easily with the help of calculated values, included in this paper, related to the amino acid composition of proteins.