  We suggest to augment standard isoelectronic focusing for separation of
proteins in a gradient of pH by a similar focusing in the presence of a
strongly charged polyelectrolyte (PE). Proteins which have the same isoelectric
point but different "hidden" charge of both signs in pI point make complexes
with PE, which focus in different pH. This is a result of charge inversion of
such proteins by adsorbed PE molecules, which is sensitive to the hidden
charge. Hence the hidden charge is a new separation parameter.
