Analytical techniques for cell fractions12XXIV. Isoelectric point standards for two-dimensional electrophoresis

We have investigated the two-dimensional electrophoretic behavior of a number of proteins throughout the course of carbamylation induced by heating in urea solution. Stepwise charge changes occur which are apparently commensurate with the number of free amino groups in the protein. Characteristic changes also occur in the sodium dodecyl sulfate (SDS) electrophoretic mobility (SDS molecular weight) of some heavily carbamylated proteins, implying altered structure or SDS binding. A mixture of all carbamylation intermediates of a protein provides a simple solution to the problem of internal isoelectric point standardization in the two-dimensional electrophoretic technique of P. H. O'Farrell (1975, J. Biol. Chem.250, 4007–4021).