POLYPEPTIDE AMINO-ACID-COMPOSITION AND ISOELECTRIC POINT .1. A CLOSED-FORM APPROXIMATION

Two analytical expressions correlating explicitly polyampholyte isoelectric point to acid-base composition are derived and presented. The utility and limitations of these equations for the determination of the isoelectric points of oligopeptides and proteins from their amino acid composition are discussed, The limiting forms of the expressions at extreme and nearly neutral compositions are obtained and the values of the isoelectric point at acid-to-base molar ratios of 1/2, 1, and 2 are calculated. (C) 1995 Academic Press, Inc.