Funnel-well SDS-PAGE: a rapid technique for obtaining sufficient quantities of low-abundance proteins for internal sequence analysis.

We report a modified sodium dodecyl sulfate polyacrylamide gel electrophoresis method that permits up to a 60-fold concentration factor, without significant loss of protein. This method leads to very efficient concentration of low-abundance proteins from partially purified fractions or very dilute protein solution. Furthermore, it permits in situ enzymatic digestion and consequently increases the probability of obtaining a suitable internal sequence.