A new analytical procedure for two-dimensional electrophoresis of cellular proteins: comparison of protein compositions of parent strain and a K+-accumulation mutant of E. coli.

An improved two-dimensional analytical electrophoretic technique fractionates according to molecular weight in the presence of dedecyl sulfate in the first dimension, then fractionates according to isoelectric point in a perpendicular dimension. Electrofocusing in the second dimension achieves nearly complete removal of most protein components while providing true estimates of their isoelectric points. Because not all proteins penetrate isoelectric focusing gels, some proteins may go unrecognized using conventional two-dimensional systems where isoelectric focusing precedes electrophoresis. However, such components do enter dodecyl sulfate gels; hence the presence and molecular weight of those components can be established by the new procedure. A concurrent finding was that, in general, penetration of isoelectric focusing gels by discrete protein subunits dissolved in 9 M urea is an all-or-none phenomenon depending on the solubility of the specific subunit. The procedure was applied to comparison of the protein compositions of a parental strain (CBH) of Escherichia coli and a derived mutant strain (RD-2) deficient in ability to accumulate K+. The strains showed similar two-dimensional patterns except for one discrete isoelectric component absent in the parent strain but present in the mutant.