FRACTIONATION OF PEPTIDES IN PROTEASE DIGESTS OF PROTEINS BY PREPARATIVE ISOELECTRIC-FOCUSING IN THE ABSENCE OF ADDED AMPHOLYTE - A BIOCOMPATIBLE AND LOW-COST APPROACH REFERRED TO AS AUTOFOCUSING

Peptides in the protease digests of some acidic and basic proteins in the range of 0.1-1.0% (w/v) could be fractionated with high reproducib ility by a preparative isoelectric focusing on the basis of the amphot eric nature of samples in the absence of added carrier ampholytes. Enr ichment of peptides of up to 15-fold could be achieved by the present method. This technique, referred to as autofocusing, did not require o r yield any toxic solvents or solutes; thus, the present approach can be a low-cost and biocompatible method for peptide fractionation.