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

Two analytical expressions correlating explicitly polyampholyte isoele ctric point to acid-base composition are derived and presented. The ut ility 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 e xtreme 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 ar e calculated. (C) 1995 Academic Press, Inc.