  Membrane and nuclear proteins of poor solubility have been separated by high
resolution two-dimensional (2-D) gel electrophoresis. Isoelectric focusing with
immobilized pH gradients leads to severe quantitative losses of proteins in the
resulting 2-D map, although the resolution is usually high. Protein solubility
could be improved by using denaturing solutions containing various detergents
and chaotropes. Best results were obtained with a denaturing solution
containing urea, thiourea, and detergents (both nonionic and zwitterionic). The
usefulness of thiourea-containing denaturing mixtures is shown for microsomal
and nuclear proteins as well as for tubulin, a protein highly prone to
aggregation.
